Align Intl.DateTimeFormat constructor with spec-mandated initialization order

[Vellumic]

This Pull Request fixes/closes #5335.

It changes the following:

• Swap the prototype lookup and DateTimeFormat creation to match the spec steps order
• Add a regression test for this specific case
• Add a step 1 from spec to create_date_time_format as well as comment about why it's missing

Validation

• Run (all passed)

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

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	53,125	53,125	0
Passed	51,072	51,072	0
Ignored	1,482	1,482	0
Failed	571	571	0
Panics	0	0	0
Conformance	96.14%	96.14%	0.00%

Tested main commit: 7ce9cae84ac9bf54fe528bb05b997ac24af808a4
Tested PR commit: 7d4e6c3a0d5208a0f4343acb1396e52016608b20
Compare commits: 7ce9cae...7d4e6c3

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 60.35%. Comparing base (6ddc2b4) to head (7d4e6c3).
⚠️ Report is 982 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #5336       +/-   ##
===========================================
+ Coverage   47.24%   60.35%   +13.10%     
===========================================
  Files         476      567       +91     
  Lines       46892    63149    +16257     
===========================================
+ Hits        22154    38113    +15959     
- Misses      24738    25036      +298     

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[Vellumic]

Hi everyone! Just wanted to gently bump this PR. Let me know if you need any changes or refactoring from my side. Thanks!