[Shortcut Guide] Add Less Than and greater than characters and fix crash if key is empty or invalid (#49562)

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- [x] Closes:  #49558
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doc/specs/WinGet Manifest Keyboard Shortcuts schema.md

@@ -235,6 +235,8 @@ By convention these tokens are written as double-quoted strings in the YAML (for
 |`<Arrow>`| Corresponds to either the left, right, up or down arrow key |
 |`<ArrowLR>`| Corresponds to either the left or right arrow key |
 |`<ArrowUD>`| Corresponds to either the up or down arrow key |
+|`<LessThan>`| Corresponds to the `<` key |
+|`<GreaterThan>`| Corresponds to the `>` key |
 |`<Underlined letter>`| Corresponds to any letter that is _underlined_ in the UI |
 
 </details>

src/modules/ShortcutGuide/ShortcutGuide.Ui/ShortcutGuideXAML/Controls/KeyVisual.xaml.cs

@@ -107,6 +107,8 @@ namespace ShortcutGuide.Controls
                     "<Arrow>" => "\uE0E2\uE0E3\uE0E4\uE0E5",
                     "<Enter>" => "\uE751",
                     "<Backspace>" => "\uE750",
+                    "<LessThan>" => "<",
+                    "<GreaterThan>" => ">",
                     "<Escape>" => "Esc",
                     string s when s.StartsWith('<') => s.Trim('<', '>'),
                     _ => key,
@@ -175,7 +177,7 @@ namespace ShortcutGuide.Controls
 
         private void SetGlyphOrText(string glyphOrText)
         {
-            this.RenderKeyAsGlyph = ((glyphOrText[0] >> 12) & 0xF) is 0xE or 0xF;
+            this.RenderKeyAsGlyph = glyphOrText.Length > 0 && ((glyphOrText[0] >> 12) & 0xF) is 0xE or 0xF;
             this._keyPresenter.Content = glyphOrText;
 
             this._keyPresenter.Style = this.RenderKeyAsGlyph