Enable oscars behind feature flags in boa_gc

[nekevss]

This PR adds an unstable and oscars feature flag and re-exports the oscars repo from boa_gc.

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	52,963	52,963	0
Passed	50,073	49,901	-172
Ignored	2,072	2,222	+150
Failed	818	840	+22
Panics	0	0	0
Conformance	94.54%	94.22%	-0.32%

Broken tests (22):

test/intl402/supportedLocalesOf-test-option-localeMatcher.js (previously Passed)
test/intl402/supportedLocalesOf-returned-array-elements-are-not-frozen.js (previously Passed)
test/intl402/supportedLocalesOf-unicode-extensions-ignored.js (previously Passed)
test/intl402/supportedLocalesOf-default-locale-and-zxx-locale.js (previously Passed)
test/intl402/supportedLocalesOf-taint-Array-2.js (previously Passed)
test/intl402/supportedLocalesOf-empty-and-undefined.js (previously Passed)
test/intl402/default-locale-is-supported.js (previously Passed)
test/intl402/supportedLocalesOf-locales-arg-empty-array.js (previously Passed)
test/intl402/supportedLocalesOf-consistent-with-resolvedOptions.js (previously Passed)
test/intl402/supportedLocalesOf-taint-Array.js (previously Passed)
test/intl402/supportedLocalesOf-locales-arg-coered-to-object.js (previously Passed)
test/intl402/supportedLocalesOf-duplicate-elements-removed.js (previously Passed)
test/intl402/language-tags-canonicalized.js (previously Passed)
test/intl402/DateTimeFormat/supportedLocalesOf/length.js (previously Passed)
test/intl402/DateTimeFormat/supportedLocalesOf/basic.js (previously Passed)
test/intl402/DateTimeFormat/supportedLocalesOf/builtin.js (previously Passed)
test/intl402/DateTimeFormat/supportedLocalesOf/name.js (previously Passed)
test/intl402/DateTimeFormat/supportedLocalesOf/prop-desc.js (previously Passed)
test/intl402/DateTimeFormat/prototype/toStringTag/toStringTag.js (previously Passed)
test/intl402/DateTimeFormat/prototype/toStringTag/toString.js (previously Passed)
test/intl402/Number/prototype/toLocaleString/throws-same-exceptions-as-NumberFormat.js (previously Passed)
test/built-ins/Object/freeze/typedarray-backed-by-resizable-buffer.js (previously Passed)

Tested main commit: 197b736bb87523a14b41834c078adbec3059d237
Tested PR commit: 2d5bddc7ac5fa0c504dd1cd4acd7f053f90768d8
Compare commits: 197b736...2d5bddc

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 59.20%. Comparing base (6ddc2b4) to head (2d5bddc).
⚠️ Report is 874 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #5115       +/-   ##
===========================================
+ Coverage   47.24%   59.20%   +11.96%     
===========================================
  Files         476      563       +87     
  Lines       46892    62793    +15901     
===========================================
+ Hits        22154    37178    +15024     
- Misses      24738    25615      +877     

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[jedel1043]

Why the unstable feature? Is it not enough to have the oscars feature to gate the new GC?