Add M3U playlist entry points and encoding support

[bubio]

Summary

• Add M3U/M3U8 file associations for Android, Linux, and macOS.
• Support opening playlists from the command line, file menu, drag-and-drop, and platform file browsers.
• Add playlist selection for assigning disk images to drives, including transactional loading and rollback.
• Support UTF-8, UTF-16, and Shift-JIS playlist files with validation.
• Add coverage for playlist loading, encodings, and invalid input handling.

Testing

• Added and updated clidisk_test cases for UTF-8 BOM, UTF-16 LE, Shift-JIS, and invalid M3U8 playlists.