This commit improves the error messages for the `deno test` async op
sanitizer. It does this in two ways:
- it uses handwritten error messages for each op that could be leaking
- it includes traces showing where each op was started
This "async op tracing" functionality is a new feature in deno_core.
It likely has a significant performance impact, which is why it is only
enabled in tests.
This change also makes the timers implementation closer to the spec, and
sets up the stage to implement AbortSignal.timeout() (whatwg/dom#1032).
Fixes #8965
Fixes #10974
Fixes #11398