Implement ephemeron-based weak map

[jedel1043]

This Pull Request fixes #2596 and fixes #2732.

It changes the following:

• Implements an ephemeron-based weak map using the hashbrown raw API.

I only exposed WeakMap as public, but it would be good to decide in the future if we want to expose the full RawWeakMap to our users.

Marking as draft since this just needs documentation and a clippy run, but it's feature complete.

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	95,282	95,282	0
Passed	74,984	74,984	0
Ignored	19,220	19,220	0
Failed	1,078	1,078	0
Panics	0	0	0
Conformance	78.70%	78.70%	0.00%

[codecov]

Codecov Report

Merging #3052 (02246b9) into main (5f70585) will increase coverage by 0.24%.
The diff coverage is 60.36%.

❗ Current head 02246b9 differs from pull request most recent head 0c43545. Consider uploading reports for the commit 0c43545 to get more accurate results

@@            Coverage Diff             @@
##             main    #3052      +/-   ##
==========================================
+ Coverage   50.40%   50.64%   +0.24%     
==========================================
  Files         436      444       +8     
  Lines       42375    42746     +371     
==========================================
+ Hits        21358    21649     +291     
- Misses      21017    21097      +80     

Files Changed	Coverage Δ
boa_engine/src/builtins/weak_set/mod.rs	14.47% <0.00%> (ø)
boa_gc/src/pointers/weak.rs	47.05% <ø> (-23.53%)	⬇️
boa_gc/src/pointers/weak_map.rs	55.10% <53.26%> (-24.90%)	⬇️
boa_gc/src/internals/ephemeron_box.rs	87.71% <100.00%> (+1.80%)	⬆️
boa_gc/src/internals/weak_map_box.rs	90.90% <100.00%> (ø)
boa_gc/src/lib.rs	99.41% <100.00%> (-0.05%)	⬇️
boa_gc/src/pointers/ephemeron.rs	95.12% <100.00%> (+2.01%)	⬆️

... and 85 files with indirect coverage changes

[HalidOdat]

Looks good to me! :)

[raskad]

Nice work