CmdPal: Enhance font icon classification and visuals (#41573)

## Summary of the Pull Request

- Introduces `FontIconGlyphClassifier` for classifying emojis and
symbols.
- Correctly recognizes multi-codepoint glyphs (e.g., 🧙🏼‍♀️ *woman mage
with medium-light skin tone*).
- Explicitly disallows multi-glyph icons (they would overflow anyway).
- Distinguishes between emojis and regular text characters (letters,
numbers, symbols), since emojis are slightly larger and require
different padding.
- Recognizes Unicode [Variation
Selectors](https://en.wikipedia.org/wiki/Variation_Selectors_(Unicode_block))
to enforce specific styles: VS15 (U+FE0E) for text style (monochrome)
and VS16 (U+FE0F) for emoji style (color). This lets developers choose
which variant to display. By default, characters with both
representations render as text/monochrome (e.g., ▶ `\u25B6`):
<img width="428" height="39" alt="image"
src="https://github.com/user-attachments/assets/c5e6865f-61de-4f45-9f3a-4e15e5e5ceb8"
/>
- Invalid icons are displayed as a dashed circle so extension developers
can spot issues, without being overly distracting if they slip into
production.

- Updates `IconPathConverter` to use the new classifier for improved
icon handling.
- Adds `SampleIconPage` to demonstrate various icon usages and
classifications.
- Adjusts icon alignment in `IconBox` so icons are centered.  
- Scales negative padding for emojis in `IconBox` with control size,
fixing misalignment and clipping (noticeable in tags and the details
pane hero image).
- Applies negative padding to all font icons. This removes the need for
classification in these cases and ensures symbols rendered below the
baseline remain visible.

Based on
[microsoft/terminal#19143](https://github.com/microsoft/terminal/pull/19143):
Co-authored-by: Dustin L. Howett <duhowett@microsoft.com>

Pictures? Pictures!

<img width="1912" height="2394" alt="image"
src="https://github.com/user-attachments/assets/05a16309-b658-4f21-8f9d-9a3f20db6ad8"
/>

Keyboard and flag/country emojis may look a bit off, but that’s how
they’re actually rendered:
<img width="482" height="95" alt="image"
src="https://github.com/user-attachments/assets/dc7d4d0d-3dc8-4df5-9b9f-9e977e7e989f"
/>


<!-- Please review the items on the PR checklist before submitting-->
## PR Checklist

- [x] Closes: 
  - #41489 
  - #41496 
- [ ] **Communication:** I've discussed this with core contributors
already. If the work hasn't been agreed, this work might be rejected
- [ ] **Tests:** Added/updated and all pass
- [ ] **Localization:** All end-user-facing strings can be localized
- [ ] **Dev docs:** Added/updated
- [ ] **New binaries:** Added on the required places
- [ ] [JSON for
signing](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ESRPSigning_core.json)
for new binaries
- [ ] [WXS for
installer](https://github.com/microsoft/PowerToys/blob/main/installer/PowerToysSetup/Product.wxs)
for new binaries and localization folder
- [ ] [YML for CI
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ci/templates/build-powertoys-steps.yml)
for new test projects
- [ ] [YML for signed
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/release.yml)
- [ ] **Documentation updated:** If checked, please file a pull request
on [our docs
repo](https://github.com/MicrosoftDocs/windows-uwp/tree/docs/hub/powertoys)
and link it here: #xxx

<!-- Provide a more detailed description of the PR, other things fixed,
or any additional comments/features here -->
## Detailed Description of the Pull Request / Additional comments

<!-- Describe how you validated the behavior. Add automated tests
wherever possible, but list manual validation steps taken as well -->
## Validation Steps Performed

src/modules/cmdpal/Microsoft.Terminal.UI/IconPathConverter.cpp

@@ -2,7 +2,7 @@
 #include "IconPathConverter.h"
 #include "IconPathConverter.g.cpp"
 
-// #include "Utils.h"
+ #include "FontIconGlyphClassifier.h"
 
 #include <Shlobj.h>
 #include <Shlobj_core.h>
@@ -110,7 +110,7 @@ namespace winrt::Microsoft::Terminal::UI::implementation
                 if (til::equals_insensitive_ascii(iconUri.Extension(), L".svg"))
                 {
                     typename ImageIconSource<TIconSource>::type iconSource;
-                    winrt::Microsoft::UI::Xaml::Media::Imaging::SvgImageSource source{ iconUri };	
+                    winrt::Microsoft::UI::Xaml::Media::Imaging::SvgImageSource source{ iconUri };
                     iconSource.ImageSource(source);
                     return iconSource;
                 }
@@ -169,41 +169,46 @@ namespace winrt::Microsoft::Terminal::UI::implementation
 
             // If we fail to set the icon source using the "icon" as a path,
             // let's try it as a symbol/emoji.
-            //
-            // Anything longer than 2 wchar_t's _isn't_ an emoji or symbol, so
-            // don't do this if it's just an invalid path.
-            if (!iconSource && iconPath.size() <= 2)
+            if (!iconSource)
             {
                 try
                 {
-                    typename FontIconSource<TIconSource>::type icon;
-                    const auto ch = til::at(iconPath, 0);
+                    const auto glyph_kind = FontIconGlyphClassifier::Classify(iconPath);
 
-                    // The range of MDL2 Icons isn't explicitly defined, but
-                    // we're using this based off the table on:
-                    // https://docs.microsoft.com/en-us/windows/uwp/design/style/segoe-ui-symbol-font
-                    const auto isMDL2Icon = ch >= L'\uE700' && ch <= L'\uF8FF';
-                    if (isMDL2Icon)
+                    winrt::hstring family;
+                    if (glyph_kind == FontIconGlyphKind::Invalid)
                     {
-                        icon.FontFamily(winrt::Microsoft::UI::Xaml::Media::FontFamily{ L"Segoe Fluent Icons, Segoe MDL2 Assets" });
+                        family = L"Segoe UI";
                     }
                     else if (!fontFamily.empty())
                     {
-                        icon.FontFamily(winrt::Microsoft::UI::Xaml::Media::FontFamily{ fontFamily });
-
+                        family = fontFamily;
+                    }
+                    else if (glyph_kind == FontIconGlyphKind::FluentSymbol)
+                    {
+                        family = L"Segoe Fluent Icons, Segoe MDL2 Assets";
+                    }
+                    else if (glyph_kind == FontIconGlyphKind::Emoji)
+                    {
+                        // Emoji and other symbols go in the Segoe UI Emoji font.
+                        // Some emojis (e.g. 2️⃣) would be rendered as emoji glyphs otherwise.
+                        family = L"Segoe UI Emoji, Segoe UI";
                     }
                     else
                     {
-                        // Note: you _do_ need to manually set the font here.
-                        icon.FontFamily(winrt::Microsoft::UI::Xaml::Media::FontFamily{ L"Segoe UI" });
+                        family = L"Segoe UI";
                     }
+
+                    typename FontIconSource<TIconSource>::type icon;
+                    icon.FontFamily(winrt::Microsoft::UI::Xaml::Media::FontFamily{ family });
                     icon.FontSize(targetSize);
-                    icon.Glyph(iconPath);
+                    icon.Glyph(glyph_kind == FontIconGlyphKind::Invalid ? L"\u25CC" : iconPath);
                     iconSource = icon;
                 }
                 CATCH_LOG();
             }
         }
+
         if (!iconSource)
         {
             // Set the default IconSource to a BitmapIconSource with a null source
@@ -326,7 +331,7 @@ namespace winrt::Microsoft::Terminal::UI::implementation
     }
 
     static winrt::Microsoft::UI::Xaml::Media::Imaging::SoftwareBitmapSource _getImageIconSourceForBinary(std::wstring_view iconPathWithoutIndex,
-                                                                                                         int index, 
+                                                                                                         int index,
                                                                                                          int targetSize)
     {
         // Try: