Improve "no-constant-condition" rule for generators

This topic has been discussed already in https://github.com/eslint/eslint/issues/1299 and https://github.com/eslint/eslint/issues/2375 but per https://github.com/eslint/eslint/issues/2375#issuecomment-299883115 I’m opening a new issue for this.

https://github.com/eslint/eslint/issues/2375#issuecomment-255137510 has introduced a proposal for handling this which seems pretty reasonable:

Bad:

while(true) {
    //...
}

Bad:

function*() {
    while(true) {
        //...
    }
    yield 'foo';
}

Good:

function*() {
    while(true) {
        yield 'foo';
    } 
}

~It should be noted that the same should also apply to async functions which have roughly similar semantics. Since both generators and async/await are starting to be adopted a lot more this topic should be revisited.~

/cc @platinumazure

[VictorHom]

If possible, can I take on this issue?

[platinumazure]

@Andarist My take on that is, just like for infinite loops, no-constant-condition can’t know when you mean to have an infinite task or not so your best bet is to use // eslint-disable-line comments on those cases.

Infinite generators, on the other hand, are a completely different animal altogether and I think we should consider enhancing no-constant-condition to allow an option to exclude infinite loops in generator functions (as long as they have yield statements in them).

So with all that said, I think I lean towards an exception for generators only.