More improvement to async Actor and replace more callbacks with promises

[HarelM]

I want to make sure that I don't mess things up so I'm keeping this PR open to see that the tests are passing.
I think I'll do most of the leftover improvements in this PR.
Let's see how big it gets.

[codecov-commenter]

Codecov Report

Attention: 20 lines in your changes are missing coverage. Please review.

Comparison is base (fe8e847) 75.19% compared to head (4e704b5) 75.21%.

Additional details and impacted files

@@               Coverage Diff               @@
##           async-actor    #3269      +/-   ##
===============================================
+ Coverage        75.19%   75.21%   +0.02%     
===============================================
  Files              241      241              
  Lines            19318    19291      -27     
  Branches          4340     4326      -14     
===============================================
- Hits             14526    14510      -16     
+ Misses            4792     4781      -11     

Files	Coverage Δ
src/render/glyph_atlas.ts	82.75% <100.00%> (ø)
src/render/image_atlas.ts	78.57% <100.00%> (ø)
src/render/image_manager.ts	46.19% <100.00%> (+0.31%)	⬆️
src/source/worker.ts	79.54% <100.00%> (ø)
src/util/actor.ts	80.61% <ø> (-0.20%)	⬇️
src/util/test/util.ts	92.53% <100.00%> (ø)
src/util/web_worker_transfer.ts	88.09% <0.00%> (ø)
src/source/worker_tile.ts	98.14% <97.40%> (+2.91%)	⬆️
src/source/vector_tile_source.ts	95.41% <88.00%> (-0.89%)	⬇️
src/render/glyph_manager.ts	92.07% <90.19%> (+0.81%)	⬆️
... and 1 more

... and 1 file with indirect coverage changes

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[HarelM]

This is now ready for review.
I've tested as much as possible, seems like things are working as expected.
The more I dig into this code the more weird things I find, and when I convert the code from callbacks to async functions I'm finding out a lot of hacks that were made a long the years, some of them I can't solve apparently.

CC: @smellyshovel @msbarry @ChrisLoer

This PR is against the actor async branch.
There is only one actor.send call left inside the ajax class, which will not part of this PR, I'm not even sure I would like to have it as part of this change in general as it might be too intrusive.

Most of the TODOs are done, there are a few left for the next days.
I hope this change will be able to be merged within a week or so.

[HarelM]

OK, I figured out the problem with the return promise, now fixed.
Aborting a request to a worker will create a pending promise, not sure what should be the right solution here, but for now I'm keeping the old behavior, when all the code is converted to promises it will be a lot easier to understand when something should return and what.
But this is out of scope of this PR.
This PR is now ready for review.

[neodescis]

Great changes. Keep them coming, @HarelM!