[test] Split up jsapi.js

[rossberg]

Instead of one monolithic test we should at least have separate tests for each "class" and for each main function in the API.

[ollelauribostrom]

@littledan Are you working on this? Would love to lend a hand if you could give me some pointers (first contribution to the spec).

[littledan]

I believe @Ms2ger has done this in the WPT repository. Probably the needed work item at this point is to upstream the new tests into this repository.

[Ms2ger]

The file has been removed (#883), so this issue can be closed.