Implement proposal nonextensible-applies-to-private

[jedel1043]

Implements the nonextensible-applies-to-private proposal.

Since it's such a small change and it's already on stage 3, I decided to not gate this behind the experimental feature.

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	50,747	50,747	0
Passed	47,966	47,966	0
Ignored	1,971	1,971	0
Failed	810	810	0
Panics	0	0	0
Conformance	94.52%	94.52%	0.00%

[codecov]

Codecov Report

❌ Patch coverage is 6.66667% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 57.48%. Comparing base (6ddc2b4) to head (d804fd7).
⚠️ Report is 611 commits behind head on main.

Files with missing lines	Patch %	Lines
core/engine/src/object/operations.rs	6.66%	14 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #4511       +/-   ##
===========================================
+ Coverage   47.24%   57.48%   +10.23%     
===========================================
  Files         476      504       +28     
  Lines       46892    57873    +10981     
===========================================
+ Hits        22154    33268    +11114     
+ Misses      24738    24605      -133     

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[HalidOdat]

Looks great! Just some minor nitpicks 😄

[linusg]

Note that this changed slightly in tc39/proposal-nonextensible-applies-to-private@52e3ccc :)