LibWeb: Implement Resource Timing

[Lubrsi]

See individual commits for details.
There are two fetch spec issues to file:

• Setting fetch timing's end time to a relative timestamp is incorrect, as Resource Timing will convert it to a relative timestamp itself (like all the other timestamps)
• A resource timing entry is not created if the end of the body is not reached and the fetch params doesn't have a consume body callback. This code produces different results in different engines and changes depending on when you read from the performance buffer:

fetch("/alwayserror").then(resp => {
    if (!resp.ok) {
        return "status_" + resp.status;
    }
    return resp.text();
}).then(() => {
    console.log(JSON.stringify(performance.getEntriesByType("resource")));
});

[tcl3]

I've not had a thorough look through the code yet, but here are some WPT results for the resource-timing tests:

Before:

Ran 129 tests finished in 80.6 seconds.
  • 7 ran as expected. 0 tests skipped.
  • 1 tests crashed unexpectedly
  • 11 tests had errors unexpectedly
  • 40 tests timed out unexpectedly
  • 105 tests had unexpected subtest results

Ran 1154 checks (1025 subtests, 129 tests)
Expected results: 115
Unexpected results: 1039                                                                                                                                                    test: 52 (1 crash, 11 error, 40 timeout)
  subtest: 987 (410 fail, 543 notrun, 34 timeout)

After:

Ran 129 tests finished in 83.1 seconds.
  • 31 ran as expected. 0 tests skipped.
  • 1 tests crashed unexpectedly
  • 9 tests had errors unexpectedly
  • 37 tests timed out unexpectedly
  • 76 tests had unexpected subtest results

Ran 793 checks (664 subtests, 129 tests)
Expected results: 374
Unexpected results: 419                                                                                                                                                     test: 47 (1 crash, 9 error, 37 timeout)
  subtest: 372 (163 fail, 184 notrun, 25 timeout)

I'm not sure why fewer subtests get executed now, I suspect http://wpt.live/resource-timing/response-status-code.html , may be timing out.

[github-actions]

Your pull request has conflicts that need to be resolved before it can be reviewed and merged. Make sure to rebase your branch on top of the latest master.

[ADKaster]

Couple comments, and I saw that there's a few AD-HOC and "Spec-Issue" comments that should probably be associated with an actual spec issue. Doesn't much matter to me if that actual link is set up in a follow-up though.

[ADKaster]

what if it's -0.0 ? do we have an is_zero helper for doubles?

[Lubrsi]

Fetch spec issues for the issues mentioned in the PR description have been filed:
whatwg/fetch#1812
whatwg/fetch#1813

[ADKaster]

I'mma just merge this. if that 0.0 thing is an issue I'm sure we'll find out eventually.