Add Alias functionality for Composers in Musicbrainz autotagger.

[NoDancing]

Description

This PR updates the MusicBrainz autotagger to check composer names against preferred aliases, applying the same logic used for localized artist name selection.

Fixes #5885.

To Do

• Documentation. (Unclear if any is needed, let me know!)
• Changelog.
• Tests. (initial implementation works; still experimenting with test coverage).

This is a simple change that appears to work correctly in practice. I’m still exploring the test suite and would appreciate feedback on whether additional tests or documentation are needed. Thanks!

[Copilot]

Pull Request Overview

This PR extends the MusicBrainz autotagger to apply preferred alias functionality to composer names, similar to how it already works for artist names. This ensures composer names are localized according to user preferences.

• Adds alias checking for composers using the existing _preferred_alias function
• Applies alias resolution to both composer names and sort names
• Maintains the same localization logic already used for artists

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
docs/changelog.rst	Documents the new composer alias functionality
beetsplug/musicbrainz.py	Implements alias checking for composers in the track_info function

[codecov]

Codecov Report

❌ Patch coverage is 44.44444% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 63.74%. Comparing base (d8d227e) to head (8c07148).

Files with missing lines	Patch %	Lines
beetsplug/musicbrainz.py	44.44%	3 Missing and 2 partials ⚠️

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[NoDancing]

Sorry if this created some spam in your inbox, I'm new to using github, but I think I addressed the mistakes in my last PR. Let me know if you want me to combine these various commits into something cleaner, or re-do anything, or start from scratch. Thank you!