testing: run vscode tests in-order

[connor4312]

Use proper mocha file load events so that order is retained (instead of running all suites in alphabetical order across the codebase)

Fixes #173016
Fixes #173015

[connor4312]

@hediet this should be good to go after the test is fixed 🙂

[hediet]

I spent some hours figuring out why the test fails and I'm still clueless.
Unfortunately, it only fails when running all tests in electron and unfortunately async stack traces don't work.

I think some test T asynchronously creates a disposable when the merge editor tests run.
However, T does not seem to dispose that disposable before the merge editor test finishes, so the merge editor tests marks it as leaking...
I did not figure out which test T is.

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Also, I don't think this is a proper fix for the linked issues. It fixes it for VS Code (but even that does not always seem to be the case), but generally jumping tests can still be an issue.

[connor4312]

This came in with other improvements necessary for snapshot tests