Convert more test suits to use lit and/or parallel test runner

[sbc100]

Running the lit tests and the spec tests is now really great.

I was recently debugging an issue with binaryen.js tests and wished they were either in lit of using the same parallel executor as the spec tests.

Should put some effort into making all the test suites use one of these two mechanism.

Presumably converting a given test suite (e.g. binaryen.js) to use the new parallel test runner from the spec test is a much smaller job than converting it to lit (i.e. none of the individual tests would even need to be touched), so that might be good thing to do for all the test suites that don't current make sense as lit.

[sbc100]

@stevenfontanella @tlively

[tlively]

I agree this would be nice. @stevenfontanella, how complicated would this be?

[stevenfontanella]

I let Gemini have a first attempt on this branch for the JS test suite which works but duplicates a good amount of code from the spec test runner. I was hoping to reduce the duplication here, and after that it should be good to go.

[stevenfontanella]

Just noticed that this issue is about all test suites, not just the JS tests. I can spend more time on this and try to get them all running in parallel. For my understanding, what's the main benefit that we're looking for here? Typically when I want to test something locally I run the spec test suite or the lit tests which both run pretty fast now, and I run the rest in CI. I'm wondering if there are other test suites that are particularly useful to make faster.

[sbc100]

The main benefits I'm looking for:

1. Universal speedups due to parallelism
2. Universal hiding of stdout/stderr by default (so my terminal is nice and tidy when the tests pass)
3. Universal ability to run just one test from a given suite (i.e. when a single test is failing I want to iterate on just that test)

[tlively]

I hope this would make CI run faster, too. The ubuntu-latest runners have 4 cores.