Pull in test262 tests

[bakkot]

Now that the frontmatter in test262 is more informative, we can distinguish between passing and failing parser tests by looking at phase.

[bakkot]

This could be done as a build step, to avoid duplication between projects.

[bakkot]

@jugglinmike, moving discussion here from the shift-parser-js issue.

This repo is now distributed as an npm package. I think if the main test262 tests were included as a build step, they wouldn't appear in this repo (except the script to download and sort them), but they would appear in the npm distribution. That would make it relatively useable for downstream projects without duplication.

[jugglinmike]

Including the tests via a build step would address the duplication problem, but
it would also introduce a new gate for consumers. They could only update their
tests when this project released a new version. We could pull the tests in from
master via a "post-install" step, but then consumers would be silently
updated for each installation.

[littledan]

Great to hear your concern for consumers here, @jugglinmike !

[jugglinmike]

Hopefully that's not too out-of-character for me :)

[RReverser]

Maybe only provide a build or test runner tool as part of this repo and then consumers can point it to any folder (e.g. git submodule to the actual test262) they want?