[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/peek/Peek.UI/Strings/en-us/Resources.resw

@@ -318,4 +318,12 @@
     <value>Length: {0}</value>
     <comment>{0} is the duration of the audio read from file metadata</comment>
   </data>
+  <data name="ContextMenu_Copy" xml:space="preserve">
+    <value>Copy</value>
+    <comment>Copy selected text to clipboard</comment>
+  </data>
+  <data name="ContextMenu_ToggleTextWrapping" xml:space="preserve">
+    <value>Toggle text wrapping</value>
+    <comment>Toggle whether text in pane is word-wrapped</comment>
+  </data>
 </root>