chore: remove git modules for better internal experience

[ematipico]

Summary

This PR removes the internal git submodules of test262, babel and Typescript. These modules were giving more issues than benefits, especially in the website repository where we have some codegen. Working with git submodules was becoming very hostile.

Instead, this PR adds a new checkout method in the coverage suite, and we use a simple git clone and git reset --hard to use the revision we need to run our coverage against.

Test Plan

This CI will fail because the main branch still uses the old method. However, I run this locally and it worked like a charm. That's why I added .gitignore inside the coverage folder.

[codspeed-hq]

CodSpeed Performance Report

Merging #3054 will not alter performance

_{Comparing chore/remove-submodules (4adca8a) with main (cd6e830)}

Summary

✅ 92 untouched benchmarks