Some optimizations for Promise handling

[jasnell]

Add some some-circuiting behavior when promises are already rejected or resolved to undefined (when possible).

We can't completely optimize every case because of silly timing differences that are introduced but this gets us at least part of the way.

[codspeed-hq]

Merging this PR will not alter performance

✅ 72 untouched benchmarks
⏩ 129 skipped benchmarks¹

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_{Comparing jasnell/promise-short-circuit (df1336a) with main (b322726)²}

Footnotes

1. 129 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

2. No successful run was found on main (9e6e5cb) during the generation of this report, so b322726 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 66.44%. Comparing base (46d402b) to head (df1336a).
⚠️ Report is 17 commits behind head on main.

Files with missing lines	Patch %	Lines
src/workerd/jsg/promise.h	0.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6645      +/-   ##
==========================================
- Coverage   66.48%   66.44%   -0.05%     
==========================================
  Files         405      405              
  Lines      117783   116102    -1681     
  Branches    19425    19431       +6     
==========================================
- Hits        78306    77141    -1165     
+ Misses      27895    27380     -515     
+ Partials    11582    11581       -1     

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