This adds a snippets pane, which can be a static pane with all your
snippets (`sendInput` actions) in it. (See #17329)

This pane has a treeview with these actions in it, that we can filter
with a textbox at the top.

Play buttons next to entries make it quick to run the command you found.

Bound in the default actions with

```json
        { "command": { "action": "splitPane", "type": "snippets" }, "id": "Terminal.OpenSnippetsPane", "name": { "key": "SnippetsPaneCommandName" } },
```

re: #1595

----

TODO, from 06-04 bug bash

* [x] Snippets pane doesn't display some "no snippets found" text if
there aren't any yet
* [x] open snippets pane; find a "send input"; click the play button on
it; input is sent to active pane; begin typing
* [x] I can open an infinite amount of suggestions panes
* ~I'm closing this as by-design for now at least. Nothing stopping
anyone from opening infinite of any kind of pane.~
* ~This would require kind of a lot of refactoring in this PR to mark a
kind of pane as being a singleton or singleton-per-tab~
  * Okay everyone hates infinite suggestions panes, so I got rid of that
* [x] Ctrl+Shift+W should still work in the snippets pane even if focus
isn't in textbox
* [ ] open snippets pane; click on text box; press TAB key;
  * [ ] If you press TAB again, I have no idea where focus went
* [x] some previews don't work. Like `^c` (`"input": "\u0003"`)
* [x] nested items just give you a bit of extra space for no reason and
it looks a little awkward
* [x] UI Suggestion: add padding on the right side
* [ ] [Accessibility] Narrator says "Clear buffer; Suggestions found
132" when you open the snippets pane
- Note: this is probably Narrator reading out the command palette (since
that's where I opened it from)
- We should probably expect something like "Snippets", then (assuming
focus is thrown into text box) "Type to filter snippets" or something
like that

We have to run in an older OneBranch Windows container image due to
compiler bugs.

This change prevents us from having to wait for the container image to
download for build legs that _aren't_ using the compiler.

* Modified `Generate-PseudoLocalizations.ps1` to find the .xml files.
  (As opposed to .resw for the other translations.)
* Added support for the new format by adding new XPath expressions,
  and stripping comments/attributes as needed.
* Fixed `PreserveWhitespace` during XML loading.
* Fixed compliance with PowerShell's strict mode.

## Validation Steps Performed
Ran it locally and compared the results. ✅

This fixes some more issues not properly covered by #17526:
* Fixed `_locComment_text` comments being effectively ignored.
* Fixed line splitting of comments (CRLF vs LF).
* Fixed BOM suppression.
* Fixed support for having multiple `{Locked=...}` comments.

This reverts commit e9212e4.

As discussed in the bug bash. It should be closable with a button. 

This also changes the tab color to match the Settings tabs.

This also fixes a crash where dragging just a snippets pane out to it's
own window would crash.