Remove immutable package

[koesie10]

This removes the immutable package since it's only used in 1 file and it's not really necessary in that file. I've rewritten the places where it's used in the simplest way possible (i.e. just replacing I.List with an array and I.Map with a standard Map). This removes approximately 175 KB from the bundled extension.js file.

Checklist

• CHANGELOG.md has been updated to incorporate all user visible changes made by this pull request.
• Issues have been created for any UI or other user-facing changes made by this pull request.
• [Maintainers only] If this pull request makes user-facing changes that require documentation changes, open a corresponding docs pull request in the github/codeql repo and add the ready-for-doc-review label there.

[charisk]

LGTM.

Shame there aren't any unit tests. Have you done any testing to confirm the change?

[koesie10]

Shame there aren't any unit tests. Have you done any testing to confirm the change?

I haven't done any manual testing because I don't know how to exactly get this code to trigger and what I should be looking for. However, this is tested by some unit tests: test/unit-tests/log-scanner.test.ts.

[charisk]

Shame there aren't any unit tests. Have you done any testing to confirm the change?

I haven't done any manual testing because I don't know how to exactly get this code to trigger and what I should be looking for. However, this is tested by some unit tests: test/unit-tests/log-scanner.test.ts.

Ah I was looking for them in a join-order.test.ts or something like that.