Implement node:test MockTracker

[jasnell]

Requires the nodejs_compat compatibility flag to be enabled.

Does not yet support mock timers.

Does not implement the full node:test module, just the mocks

Refs: https://nodejs.org/docs/latest/api/test.html#class-mocktracker

Implementation was adapted directly from Node.js implementation. Only changes necessary to make it work in workers were made. Majority of new lines are the tests (which were also adapted directly from Node.js' tests). The API and implementation here are intended to match Node.js'.

While this could likely be polyfilled fairly easily, building it into the runtime allows us to take advantage of it for our own tests, much like we've started to do with node:assert

[fhanau]

• Does MockTimers need TS bindings?
• MockTimers is Stability: 1 - Experimental and may have an unstable API – does this need to be guarded by e.g. an experimental flag or does nodejs_compat cover cases like this?
• Tests look good, local mocks are auto restored after the test finishes wasn't adopted but I assume that's intentional.

LGTM otherwise, seems pretty helpful for developers to me.

[jasnell]

I wasn't planning on implementing MockTimers for a while. I think just omitting those bits makes the most sense. I'll add todo comments.

Not porting that one test was intentional. The way it is structured it would need to be rewritten since wd-test has no concept of subtests/before/after etc so I wanted to look at it separately.