Use Intl.Locale over @formatjs/intl-locale

[fredrikekelund]

Related issues

• N/A

How AI was used in this PR

To verify that the Intl.Locale constructor throws in the same way that the Locale constructor from @formatjs/intl-locale does.

Proposed Changes

• Uninstall the @formatjs/intl-locale npm module and replace our (very simple) use of the Locale constructor with the standard library Intl.Locale constructor (MDN). @formatjs/intl-locale is indeed a polyfill for Intl.Locale (ref).
• Before this change, the @formatjs namespace took up 323kB in the CLI JS bundle. After this change, only @formatjs/intl-localematcher remains, which takes up 46kB.
• I also took the opportunity to explicitly list @formatjs/intl-localematcher as a dependency in apps/cli (and to update that dependency).

Testing Instructions

CI should pass.

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors?

[wpmobilebot]

📊 Performance Test Results

Comparing 3ed493f vs trunk

app-size

Metric	trunk	3ed493f	Diff	Change
App Size (Mac)	1358.10 MB	1354.70 MB	3.40 MB	🟢 -0.3%

site-editor

Metric	trunk	3ed493f	Diff	Change
load	1675 ms	1624 ms	51 ms	🟢 -3.0%

site-startup

Metric	trunk	3ed493f	Diff	Change
siteCreation	9033 ms	9039 ms	+6 ms	⚪ 0.0%
siteStartup	4417 ms	4417 ms	0 ms	⚪ 0.0%

---

Results are median values from multiple test runs.

Legend: 🟢 Improvement (faster) | 🔴 Regression (slower) | ⚪ No change (<50ms diff)

[bcotrim]

LGTM 👍