Fix a spec violation in Date.prototype.toLocaleString

[Vellumic]

This Pull Request fixes/closes #5323

Changes

• Eliminates the code which broke the standard behavior, when calling Date.prototype.toLocaleString with dateStyle/timeStyle options.
• Adds a regression test to ensure that dateStyle and timeStyle don't force a fallback to a combined date-time string, as per ECMA-402

Validation

• Run (all passed)

cargo test --package boa_engine --lib --features intl_bundled -- builtins::intl::date_time_format::tests --nocapture

• Manual check

>> const date = new Date(Date.UTC(2024, 2, 10, 2, 30))
undefined
>> date.toLocaleString("en-US", {dateStyle: "short"})
"3/10/24"
>> date.toLocaleString("en-US", {timeStyle: "short"})
"2:30\u{202f}AM"

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	53,125	53,125	0
Passed	51,049	51,049	0
Ignored	1,482	1,482	0
Failed	594	594	0
Panics	0	0	0
Conformance	96.09%	96.09%	0.00%

Tested main commit: 3cec5e6bc4454077cb8d65b537d368d633137e0e
Tested PR commit: ff676cda6e326dae77479ffb6b12a73d6ed25456
Compare commits: 3cec5e6...ff676cd

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 59.85%. Comparing base (6ddc2b4) to head (ff676cd).
⚠️ Report is 951 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #5324       +/-   ##
===========================================
+ Coverage   47.24%   59.85%   +12.60%     
===========================================
  Files         476      590      +114     
  Lines       46892    63683    +16791     
===========================================
+ Hits        22154    38115    +15961     
- Misses      24738    25568      +830     

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[HalidOdat]

Looks good to me! 😄