WIP: Add webview output experience

[bpringe]

What has changed?

A new webview for REPL output is added. It will be a new output location in settings. This is still in the exploratory phase (sort of). I'm opening this draft PR now for visibility and also so I can use it quickly gain context again when I pick this work up here and there as I have time. I'm exploring unknowns and potential problem areas before spending much time on stuff we know we can do.

Once this is in a usable state I plan to dogfood it for a while before releasing it.

This is also an experiment in adding a new feature almost completely in cljs, which utilizes the VS Code API.

Closes #2480

My Calva PR Checklist

I have:

• [x] Read How to Contribute.
• [x] Directed this pull request at the dev branch. (Or have specific reasons to target some other branch.)
• [x] Made sure I have changed the PR base branch, so that it is not published. (Sorry for the nagging.)
• [x] 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.
• [ ] 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

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[PEZ]

Shall we try to release this behind an opt-in setting as quickly as we can?

[bpringe]

Shall we try to release this behind an opt-in setting as quickly as we can?

Sorry, I'm moving slowly with this so far due to being busy with other life things. It's not quite ready but there's not that much more to do before getting it to a very basic usable state. I've started dedicating a little focused dev time on weekends for this.