Use downcast on Date intrinsic to ensure borrows are not extended

[jedel1043]

Stacked on #5489.

Makes it harder to have double borrows if the borrows are immediately dropped.

Bug found by @Yanhaoxi

[github-actions]

Test262 conformance changes

Test result	main count	PR count	difference
Total	53,125	53,125	0
Passed	51,083	51,083	0
Ignored	1,482	1,482	0
Failed	560	560	0
Panics	0	0	0
Conformance	96.16%	96.16%	0.00%

Tested main commit: 14846ead8fff8312fefa50deb6a64ede8584d7f3
Tested PR commit: ca7c8fb7e52c66fa4318f661c151c87d41d12044
Compare commits: 14846ea...ca7c8fb

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 62.79%. Comparing base (6ddc2b4) to head (ca7c8fb).
⚠️ Report is 1020 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #5492       +/-   ##
===========================================
+ Coverage   47.24%   62.79%   +15.54%     
===========================================
  Files         476      530       +54     
  Lines       46892    59064    +12172     
===========================================
+ Hits        22154    37089    +14935     
+ Misses      24738    21975     -2763     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.