Implement custom text context menus to fix crashes (#18854)

This works around a bug in WinUI where it creates a single context
menu/flyout for text elements per thread, not per `XamlRoot`, similar to
many other areas. Since the `XamlRoot` cannot change after creation,
this means that once you've opened the flyout, you're locked into that
window (= XAML root) forever. You can't open the flyout in another
window and once you've closed that window, you can't open it anywhere at
all.

Closes #18599

## Validation Steps Performed
* Flies out right click in the
  * About dialog ✅
  * Search dialog ✅
  * Word delimiters setting ✅
  * Launch size setting ✅
* Across two windows ✅

.github/actions/spelling/expect/expect.txt

@@ -128,6 +128,7 @@ Blt
 blu
 BLUESCROLL
 bmi
+bodgy
 BODGY
 BOLDFONT
 Borland
@@ -371,8 +372,8 @@ Dcd
 DColor
 dcommon
 DComposition
-dde
 DDDCCC
+dde
 DDESHARE
 DDevice
 DEADCHAR