fix(engine): Prefer js_error! over JsError::from_opaque

[p0lyw0lf]

In a few places, native code was throwing
JsError::from_opaque(js_string!("some literal")). This is allowed, but it is not exactly standard: most users will expect thrown values to be of type Error.

So, where possible, let's convert code using that to instead use the provided js_error! macro, which does generate proper Error objects.

This doesn't touch AbortError, because (1) that's a larger code change, and (2) it might actually be relied on as a sentinel value.

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	52,963	52,963	0
Passed	50,073	50,073	0
Ignored	2,072	2,072	0
Failed	818	818	0
Panics	0	0	0
Conformance	94.54%	94.54%	0.00%

Tested main commit: 197b736bb87523a14b41834c078adbec3059d237
Tested PR commit: e5bd33f426546531ea323801867d5a6d2bb77963
Compare commits: 197b736...e5bd33f

[codecov]

Codecov Report

❌ Patch coverage is 25.00000% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 59.30%. Comparing base (6ddc2b4) to head (e5bd33f).
⚠️ Report is 874 commits behind head on main.

Files with missing lines	Patch %	Lines
core/engine/src/module/loader/mod.rs	42.85%	4 Missing ⚠️
core/engine/src/builtins/date/mod.rs	0.00%	3 Missing ⚠️
core/engine/src/interop/into_js_function_impls.rs	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #5116       +/-   ##
===========================================
+ Coverage   47.24%   59.30%   +12.06%     
===========================================
  Files         476      563       +87     
  Lines       46892    62785    +15893     
===========================================
+ Hits        22154    37235    +15081     
- Misses      24738    25550      +812     

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