Fix: Only auto register settings if the plugin the connector references is installed and active.

[jorgefilipecosta]

Summary

• keep connector setting auto-registration unchanged for AI providers
• only auto-register non-AI connector settings when plugin.is_active exists, is callable, and returns true
• add focused PHPUnit coverage for the AI and non-AI registration paths
• The current behavior is wrong if plugin A registers a connector for plugin B we were having a bug where its settings were registered and exposed in REST even if plugin B was not installed and activated. This fixes the issue.

Testing

• Verify the connectors page works as before.
• Verify the unit tests pass.

[github-actions]

Flaky tests detected in 933f28b.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/24355536206
📝 Reported issues:

• [Flaky Test] post title and content are editable and blocks can be inserted #76524 in /test/e2e/specs/editor/various/post-content-focus-mode.spec.js
• [Flaky Test] should show correct homepage actions based on current homepage or posts page #77385 in /test/e2e/specs/site-editor/homepage-settings.spec.js

[github-actions]

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Co-authored-by: jorgefilipecosta <jorgefilipecosta@git.wordpress.org>
Co-authored-by: t-hamano <wildworks@git.wordpress.org>

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[t-hamano]

Can we create a core ticket and a core PR to move this PR forward?

[jorgefilipecosta]

Can we create a core ticket and a core PR to move this PR forward?

It was already done WordPress/wordpress-develop#11564, https://core.trac.wordpress.org/ticket/65099 as soon as WordPress/wordpress-develop#11565 is committed these ones will also go.