Healer module

[pbwolf]

Dear @PEZ , is this the kind of module or modularity you had in mind, with respect to extracting the whitespace edits from a reformatted result? For simplicity to clarify the goal, this PR extracts the clever healing and removal-of-plasters from format.ts into a module and adds tests for it.

What has changed?

• A module is extracted from format.ts to clarify healing/unhealing as a testable unit. (Healing an unformatted code fragment prepends and appends brackets to make it syntactically plausible enough to be submitted to a program-code formatter. After the well-formed code block has been processed by a source-code formatter, unhealing rips off the fabricated brackets and fixes up indentation of lines after the first one, to make a drop-in formatted replacement for the original fragment.)
• Tests are added for the healer module.

This is inspired by a comment by @PEZ on PR #2741

//Fixes #

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.
• 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]

Awesome. Yes, this is exactly the kind of extraction I meant.

Please update the changelog and we can merge this.

[PEZ]

Thanks! 🙏

Generally we want an issue describing the problem statement that is closed by the PR. In this case maybe it was development internal (but we usually create issues for that as well). This time I solved it by linking the changelog entry to the PR. This way if someone later runs into issues and suspects this change, they can easily find the commits.