timers: clean up, async integration for unref, simplify clearTimeout

[apapirovski]

Assorted, small changes to timers:

1. A recent commit removed the usage of the second argument of tryOnTimeout but left the definition in place. Remove it.

2. It's possible for user-code to flip an existing timeout to be an interval during its execution, in which case the current code would crash due to start being undefined. Fix this by providing a default start value within rearm.

3. When async hooks integration for Timers was introduced, it was not included in the code for unref'd or subsequently ref'd timers which means those timers only have TIMERWRAP hooks.

4. Remove dead code from timeout & interval clearing — timer[kOnTimeout] is not something that can exist, as kOnTimeout only exists on TimerWrap.

The first two commits are semver-major as they rely on several prior semver-major PRs, the other two can both go into 8.x & 9.x and I will handle back-porting these sometime later this month.

Benchmark results:

 timers/timers-breadth.js thousands=5000                    -0.49 %       ±3.13%   ±4.13%   ±5.31%
 timers/timers-cancel-pooled.js millions=5          ***   1643.69 %      ±84.28% ±111.55% ±144.05%
 timers/timers-cancel-unpooled.js millions=1        ***    101.54 %       ±9.13%  ±12.06%  ±15.51%
 timers/timers-depth.js thousands=1                         -0.01 %       ±0.09%   ±0.12%   ±0.15%
 timers/timers-insert-pooled.js millions=5                   0.43 %       ±2.05%   ±2.71%   ±3.48%
 timers/timers-insert-unpooled.js millions=1                 0.80 %       ±3.13%   ±4.13%   ±5.30%
 timers/timers-timeout-pooled.js millions=10                -2.38 %       ±4.92%   ±6.49%   ±8.34%

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• commit message follows commit guidelines

Affected core subsystem(s)

timers, test

[apapirovski]

CI: https://ci.nodejs.org/job/node-test-pull-request/12953/
Benchmark CI: https://ci.nodejs.org/view/Node.js%20benchmark/job/benchmark-node-micro-benchmarks/114/

[mcollina]

LGTM. This does not surprise me, considering the my other PR in the same area.

Good work!

[apapirovski]

Landed in 1b05d7b, 568b6a5, c11cb03, and 8204b0f

[MylesBorins]

Should this be backported to v9.x-staging? If yes please follow the guide and raise a backport PR, if not let me know or add the dont-land-on label.

[MylesBorins]

Should this be backported to v8.x-staging? If yes please follow the guide and raise a backport PR, if not let me know or add the dont-land-on label.