Move Notebooks file association to a separate extension

[PEZ]

Because of Calva Clojure Notebooks interfering with LiveShare sessions:

• Guest opens Clojure file as a notebook (incorrectly) microsoft/live-share#4765

I have moved the Notebook file association part of the Calva extension manifest over to a separate extension, Calva Spritz. It only provides these associations, and nothing else. All Notebook supporting code remains in Calva. Calva Spritz is downloaded and enabled together with Calva. Once the LiveShare team fixes that bug, we can move the file associations back to Calva.

• Fixes LiveShare participants incorrectly opening every Clojure file as if via "Open with Notebook" #1850

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.)
• 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.
• 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
• 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

[Cyrik]

Seems like a great idea!