refactor: migrate AppMetadataController to @metamask/messenger

[mikesposito]

Explanation

This PR migrates the AppMetadataController class to the new @metamask/messenger comm system, as opposed to the one exported from @metamask/base-controller.

References

• Related to Implement messenger delegation #5626

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed, highlighting breaking changes as necessary
• I've prepared draft pull requests for clients and consumer packages to resolve any breaking changes

---

Note

Migrates AppMetadataController to the new @metamask/messenger, updates metadata flag names, and aligns tests and configs with base-controller/next.

• App Metadata Controller:
  • Migrate from RestrictedMessenger (@metamask/base-controller) to Messenger (@metamask/messenger); update types and construction of namespaced messengers in tests.
  • Update imports to @metamask/base-controller/next and use BaseController from next.
  • Rename metadata flag anonymous to includeInDebugSnapshot; update deriveStateFromMetadata usages.
  • Add dependency @metamask/messenger and update TS references (tsconfig.json, tsconfig.build.json).
  • Update CHANGELOG.md with BREAKING changes.
• Docs/Repo:
  • README dependency graph: add app_metadata_controller --> messenger link.

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[mcmire]

LGTM!

[mcmire]

It's unclear to me why the code scanner workflow is failing. I don't see any issues.

[mcmire]

LGTM!

[cryptodev-2s]

LGTM!