Make options hook async

[TomerAberbach]

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• no

Breaking Changes?

• yes (breaking changes will not be merged unless absolutely necessary)
• no

List any relevant issue numbers: Closes #3397

Description

Makes the options plugin hook async, sequential instead of sync, sequential so that asynchronous work can be done in the options hook. This is useful because sometimes plugins need to modify the input options, but need to do some asynchronous work to get the necessary information to modify the input options (e.g. access the file system, make a network request, #3397, etc.)

options plugin hooks written before this change will still work because the next options hook in a chain of options hooks is always passed the resolved value of the previous options hook's promise (or just the value of the hook didn't return a promise). I can't think of why an options plugin hook would have been written before this change that returns a promise and expects the next promise hook to receive the unwrapped promise.

[codecov]

Codecov Report

Merging #3660 into master will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #3660   +/-   ##
=======================================
  Coverage   96.70%   96.70%           
=======================================
  Files         183      183           
  Lines        6287     6287           
  Branches     1832     1832           
=======================================
  Hits         6080     6080           
  Misses        105      105           
  Partials      102      102           

Impacted Files	Coverage Δ
src/rollup/rollup.ts	100.00% <100.00%> (ø)

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[lukastaegert]

Thanks, really nice work, I have nothing to add here! Will release this right away.

[lukastaegert]

I can't think of why an options plugin hook would have been written before this change that returns a promise and expects the next promise hook to receive the unwrapped promise

If you mean that the next hook would receive the promise as an argument, no, that is definitely not something we would do as it would also differ in behaviour form all other async hooks. The idea is always that you can write something completely sync in an async hook. transform would be an example where a value is reduced by async hooks that also works like you implemented it.