noslash

[gabritto]

This PR adds the basics of fourslash tests to Corsa.

• There's now a fourslash package with the basic setup for running fourslash tests.
  • The new fourslash setup creates a server and talks to it, so this would be closer to "fourslash server" tests in Strada. I think we won't need the non-server tests.
• There's a script for converting between Strada fourslash in internal/fourslash/_scripts/convertFourslash.mts.
  • You can do npm run convertfourslash to run the script.
  • The script optionally takes in a file containing a list of Strada tests to translate. This is useful when working on the script to make it attempt to translate only tests that are related to e.g. completions.
  • The script outputs a list of files it failed to parse, and it logs the reason things failed to stderr.
  • Generated tests that currently fail are skipped via t.Skip(). The current list of tests expected to fail is in internal/fourslash/_scripts/failedTests.txt.

Didn't yet include all the generated tests in the PR because it'd break GitHub.
Included example of a test the script generates: https://github.com/microsoft/typescript-go/pull/991/files#diff-9c51d0662c595fdc5d7eb5e3521e692c744a7711906f1bcceee767b32cfb9252R11

Planning to do in future PRs:

• CI action to verify that the checked-in generated fourslash tests match what the script generates.

• Better panic handling for the server, and better error message for fourslash tests when server panics.
  For reference, here's what a panic in the server currently looks like:
  

• Improve script to parse more completions tests.

• Completion baselines.

@iisaduan is working on handling ranges.

[gabritto]

Race mode test failure should be fixed by #1075.