Paredit Multicursor - Testing Utils - textNotation changes and diagnostic utils

[riotrah]

What has changed?

Prepares testing utilites for multiple selection tests, editing some existing tests to fit, while preserving their single-cursor semantics. (re)introduces the diagnostic Calva commands for creating textNotations from vscode buffers and vice versa.

• This requires changing the textNotation syntax somewhat ->
  • | for single cursor is still fine, but subsequent cursors are |1, |2, …|n, and selections now >,>1, >|2, …>n & <|…<n, instead of |>|
• Also introduces some tests for the textnotation stuff.
• The above changes required some extensions to ModelEditSelection and EditableModel.

Fixes #2417
FIxes #2418
Addresses #610

My Calva PR Checklist

I have:

• Read How to Contribute.
• Directed this pull request at the dev branch. (Or have specific reasons to target some other branch.)
• Made sure I have changed the PR base branch, so that it is not published. (Sorry for the nagging.)
• Made sure there is an issue registered with a clear problem statement that this PR addresses, (created the issue if it was not present).
  • Updated the [Unreleased] entry in CHANGELOG.md, linking the issue(s) that the PR is addressing.
  • Referenced the issue I am fixing/addressing in a commit message for the pull request.
    • If I am fixing the issue, I have used GitHub's fixes/closes syntax
    • If I am fixing just part of the issue, I have just referenced it w/o any of the "fixes” keywords.
• Figured if anything about the fix warrants tests on Mac/Linux/Windows/Remote/Whatever, and either tested it there if so, or mentioned it in the PR.
• Added to or updated docs in this branch, if appropriate
• Tests
  • Tested the particular change
  • Figured if the change might have some side effects and tested those as well.
• Formatted all JavaScript and TypeScript code that was changed. (use the prettier extension or run npm run prettier-format)
• Confirmed that there are no linter warnings or errors (use the eslint extension, run npm run eslint before creating your PR, or run npm run eslint-watch to eslint as you go).

Ping @PEZ, @bpringe, @corasaurus-hex, @Cyrik

[netlify]

✅ Deploy Preview for calva-docs ready!

Name	Link
🔨 Latest commit	2f80256
🔍 Latest deploy log	https://app.netlify.com/sites/calva-docs/deploys/65eb08313512020008a37354
😎 Deploy Preview	https://deploy-preview-2419--calva-docs.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.

[riotrah]

@PEZ I only made the GH issues as I was drafting the PR, so no commit msg references :/ - I'll get there 😅