fix(builtins/proxy,json,uri): convert panics to EngineError::Panic using js_expect

[KaustubhOG]

part of #3241.

It changes the following:

• src/builtins/proxy/mod.rs: converted 16 panics (14× downcast_ref on non-proxy object, 1× downcast_mut on revocable proxy, 2× CreateDataPropertyOrThrow) to use js_expect
• src/builtins/json/mod.rs: converted 7 panics (2× CreateDataPropertyOrThrow, 2× EnumerableOwnPropertyNames, 1× ToString on number, 1× ToIntegerOrInfinity, 1× ToString in serialize) to use js_expect
• src/builtins/uri/mod.rs: converted 1 panic (code_unit_at bounds check in encode) to use js_expect

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	52,963	52,963	0
Passed	49,666	49,666	0
Ignored	2,284	2,284	0
Failed	1,013	1,013	0
Panics	0	0	0
Conformance	93.77%	93.77%	0.00%

Tested main commit: 6bd8334d35c418e2b497f05497b05ea421ce00b7
Tested PR commit: e22fa854b953666fe3462aabd348997b55529ca7
Compare commits: 6bd8334...e22fa85

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 57.81%. Comparing base (6ddc2b4) to head (e22fa85).
⚠️ Report is 774 commits behind head on main.

Files with missing lines	Patch %	Lines
core/engine/src/builtins/proxy/mod.rs	0.00%	1 Missing ⚠️
core/engine/src/builtins/uri/mod.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #4925       +/-   ##
===========================================
+ Coverage   47.24%   57.81%   +10.56%     
===========================================
  Files         476      556       +80     
  Lines       46892    60781    +13889     
===========================================
+ Hits        22154    35138    +12984     
- Misses      24738    25643      +905     

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