Add support for Monaco Editor

[ryan6416]

This pull request adds support for the Monaco Editor. This resolves issue #140, which requested the ability to use GhostText with the Monaco Editor.

The changes include a new condition in the unsafe-messenger.js file that checks for the existence of the monaco object, and a new function monacoEditor(target) that handles the events and value transfer for the Monaco Editor.

This has been tested and confirmed to work with the Monaco Editor, and should not affect the existing support for CodeMirror and Ace.

Here's a demo of the update:

https://user-images.githubusercontent.com/12979345/214165120-d559ea7e-8ebd-4083-9f0e-a3fbdcbc3bab.mp4

[ryan6416]

Thank you for the PR! Can you add a Monaco editor to the demo page on the demo/testing page? ghosttext.fregante.com/test The "edit" link is at the bottom

Done @fregante https://github.com/fregante/ghosttext.fregante.com/pull/10

[fregante]

Refer to https://github.com/fregante/GhostText/blob/main/contributing.md#adding-support-for-more-editors for more information if you haven't.

Linting is still failing here as well and it should pass for this PR to be merged

[fregante]

You marked some of my comments as resolved but you did not address them. Please review again

[fregante]

Fixed:

• multiple field support
• selector/lint/syntax errors

Not fixed:

• see unresolved reviews, the most important broken part is that it only works "one way" (editor -> browser)

[fregante]

@ryan-efendy are you able to finish this soon? I'd love to include it in this week’s release, otherwise it'll have to wait longer