chore: fix the composer normalize check and remove PhpMetrics

[paulbalandan]

Description
The composer normalize check has been a silent no-op since #9047 moved the plugin into utils. Each step logs Command "normalize" is not defined., but echo "$(composer normalize)" always exits 0.

• Move the check to its own workflow. It runs only when a composer.json changes.
• Run the plugin from utils with --dry-run, which fails on an unnormalized file. Also check utils/composer.json.
• Remove PhpMetrics. It is unused in CI, undocumented, and pinned to a release candidate.

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value (without duplication)
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide