[Peek][PreviewPane]Show Copy entry in right-click copy menu (#33845)

## Summary of the Pull Request
Fixes two bugs:
- Peek: Missing "Copy" menu-item for all WebView2 previewers.
- PreviewPane: Missing "Copy" menu-item for markdown files only.

## Detailed Description of the Pull Request / Additional comments
The issues are:
- Peek: 
- When not using Monaco (markdown, html) - the default WebView2 context
menu has been disabled. I have enabled it and then disabled ALL
menu-items other than "Copy" (such as "Back").
- When using Monaco + Release (other code files) - current code tries to
use the Monaco context menu, but it is somehow disabled at runtime. I
spent MANY hours trying to find out why but without success. It works
fine when I view the generated html + js files in a browser or in a
Debug build or in PreviewPane. But I couldn't find the root cause.
Trying to fix it by enabling the WebView2 context menu instead doesn't
work as for whatever reason, WebView2 doesn't generate a "Copy"
menu-item (it thinks there's no selected text when there is). So in this
case, the only thing I could get to work was generating context
menu-items via WebView2 callbacks that call JS functions. As a bonus,
this way of doing it also allows "Toggle text wrapping" to work.
- PreviewPane:
- Markdown - the default WebView2 context menu has been disabled. Like
for Peek, I have enabled it and then disabled ALL menu-items other than
"Copy" (such as "Back").
- Monaco (other code files) - this already just works fine, so I've left
it as is. I *could* make it work the same way as I've done for Peek for
consistency, but I've chosen to leave it as is since it works.
  

![image](https://github.com/user-attachments/assets/d758ada7-bb62-4f40-bef7-ad08ffb83786)

![image](https://github.com/user-attachments/assets/4e0baa7e-632f-412a-b2b1-b9f666277ca7)

src/modules/previewpane/MarkdownPreviewHandler/MarkdownPreviewHandlerControl.cs

@@ -143,7 +143,7 @@ namespace Microsoft.PowerToys.PreviewHandler.Markdown
                         await _browser.EnsureCoreWebView2Async(_webView2Environment).ConfigureAwait(true);
                         _browser.CoreWebView2.SetVirtualHostNameToFolderMapping(VirtualHostName, AssemblyDirectory, CoreWebView2HostResourceAccessKind.Deny);
                         _browser.CoreWebView2.Settings.AreDefaultScriptDialogsEnabled = false;
-                        _browser.CoreWebView2.Settings.AreDefaultContextMenusEnabled = false;
+                        _browser.CoreWebView2.Settings.AreDefaultContextMenusEnabled = true;
                         _browser.CoreWebView2.Settings.AreDevToolsEnabled = false;
                         _browser.CoreWebView2.Settings.AreHostObjectsAllowed = false;
                         _browser.CoreWebView2.Settings.IsGeneralAutofillEnabled = false;
@@ -162,6 +162,23 @@ namespace Microsoft.PowerToys.PreviewHandler.Markdown
                             }
                         };
 
+                        _browser.CoreWebView2.ContextMenuRequested += (object sender, CoreWebView2ContextMenuRequestedEventArgs args) =>
+                        {
+                            var menuItems = args.MenuItems;
+
+                            if (!menuItems.IsReadOnly)
+                            {
+                                var copyMenuItem = menuItems.FirstOrDefault(menuItem => menuItem.Name == "copy");
+
+                                menuItems.Clear();
+
+                                if (copyMenuItem != null)
+                                {
+                                    menuItems.Add(copyMenuItem);
+                                }
+                            }
+                        };
+
                         // WebView2.NavigateToString() limitation
                         // See https://learn.microsoft.com/dotnet/api/microsoft.web.webview2.core.corewebview2.navigatetostring?view=webview2-dotnet-1.0.864.35#remarks
                         // While testing the limit, it turned out it is ~1.5MB, so to be on a safe side we go for 1.5m bytes

src/modules/previewpane/MonacoPreviewHandler/MonacoPreviewHandlerControl.cs

@@ -396,6 +396,7 @@ namespace Microsoft.PowerToys.PreviewHandler.Monaco
             _html = FilePreviewCommon.MonacoHelper.ReadIndexHtml();
             _html = _html.Replace("[[PT_LANG]]", _vsCodeLangSet, StringComparison.InvariantCulture);
             _html = _html.Replace("[[PT_WRAP]]", _settings.Wrap ? "1" : "0", StringComparison.InvariantCulture);
+            _html = _html.Replace("[[PT_CONTEXTMENU]]", "1", StringComparison.InvariantCulture);
             _html = _html.Replace("[[PT_THEME]]", Settings.GetTheme(), StringComparison.InvariantCulture);
             _html = _html.Replace("[[PT_STICKY_SCROLL]]", _settings.StickyScroll ? "1" : "0", StringComparison.InvariantCulture);
             _html = _html.Replace("[[PT_FONT_SIZE]]", _settings.FontSize.ToString(CultureInfo.InvariantCulture), StringComparison.InvariantCulture);