Add check for reference-compared literals to JS files

[Jack-Works]

I don't know where I can add a test for JS files.

According to discussion in #45978, I open this PR to also check JavaScript files.

[typescript-bot]

This PR doesn't have any linked issues. Please open an issue that references this PR. From there we can discuss and prioritise.

[sandersn]

Plain JS tests are in $ts/tests/cases/conformance/salsa/plainJS*. You can get the settings you need to test them from the existing tests.

A couple of gotchas I thought of:

• "[object Object]" == {}
• { toString() { return 'hi' }, valueOf() { return 'no' } } == { toString() { return 'no' }, valueOf() { return 'hi' } }

At least, I think there are shenanigans possible with valueOf; I couldn't get a working example.

[Jack-Works]

I think there's no need to support the first case. The second case is a bit more interesting, maybe I can add detection to check if the literal contains toString, valueOf, or any computed property name only in JS.

[Jack-Works]

Add test files.

[sandersn]

A couple more examples from @bradzacher's comment:

[1,2,3]=='1,2,3'// -> true({toString(){return1}})==1// -> true

The second one is pretty close to the second example in my comment but arguably more likely to be written as a weird workaround for something. Even a weird workaround shouldn't have an error in JS given the reaction of some JS users when an unavoidable red squiggly shows up.

[Jack-Works]

So we only emit it for === not for ==?

[sandersn]

Yeah, I think so.

[Jack-Works]

done

[Jack-Works]

rebased

[sandersn]

Almost ready, just one more change.

It's been a long time, so if you want me to finish this, let me know.