feat(intl): implement Temporal.Instant.prototype.toLocaleString

[JkrishnaD]

This Pull Request fixes/closes #5087.

It changes the following:

• Implements steps 1 & 2 of the spec: validates this is a Temporal.Instant object
• Accepts locales and options arguments (previously ignored with _)
• Falls back to to_ixdtf_string_with_provider until Intl.DateTimeFormat integration is complete
• Removes the vague TODO: Update for ECMA-402 compliance comment.

Full Intl.DateTimeFormat integration (steps 3 & 4) is blocked on #5080, which adds format_date_time_locale and FormatDefaults::All. Once that merges, this can be updated to use that function directly.

Spec: https://tc39.es/proposal-temporal/#sec-temporal.instant.tolocalestring

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	52,963	52,963	0
Passed	50,070	50,070	0
Ignored	2,072	2,072	0
Failed	821	821	0
Panics	0	0	0
Conformance	94.54%	94.54%	0.00%

Tested main commit: 3016f492d02a06033e11269fdcef603d293222c4
Tested PR commit: ceab2130bac11923ce54e63089ddc7cca2b28c70
Compare commits: 3016f49...ceab213

[codecov]

Codecov Report

❌ Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 59.65%. Comparing base (6ddc2b4) to head (84da348).
⚠️ Report is 921 commits behind head on main.

Files with missing lines	Patch %	Lines
core/engine/src/builtins/temporal/instant/mod.rs	0.00%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #5096       +/-   ##
===========================================
+ Coverage   47.24%   59.65%   +12.41%     
===========================================
  Files         476      589      +113     
  Lines       46892    63473    +16581     
===========================================
+ Hits        22154    37866    +15712     
- Misses      24738    25607      +869     

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[JkrishnaD]

@jedel1043 this pr is just a base and waiting for the #5080 get merged as in that we get to_locale_string which we can use directly in here

[jedel1043]

Marking as blocked on #5080

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	52,963	52,963	0
Passed	50,735	50,737	+2
Ignored	1,426	1,426	0
Failed	802	800	-2
Panics	0	0	0
Conformance	95.79%	95.80%	+0.00%

Fixed tests (2):

test/intl402/Temporal/Instant/prototype/toLocaleString/default-includes-time-not-time-zone-name.js (previously Failed)
test/intl402/Temporal/Instant/prototype/toLocaleString/dateStyle.js (previously Failed)

Tested main commit: f5e88de558e038f0ae675a012d59917a098f44b6
Tested PR commit: 9e44160994108136bf40c53a846efd480ebd8328
Compare commits: f5e88de...9e44160

[Vellumic]

Hey! Just a heads-up: my PR #5199 is already in progress and it adds the needed core logic. I've also change the signature of function you're using.

It's better to wait for my merge to avoid conflicts.
Cheers!

[JkrishnaD]

Hey @Vellumic thanks for the heads up.

So, can you ping me when your part is done.