Rename Muse Sounds profile to MuseSounds (with compat)

[cbjeukendrup]

Originally I thought about separating the UI display name from the code that's stored in the file, but that seemed to be more work than the solution of this PR. And since it's still not very clear which way we want to go with these profiles, I'd prefer not spending too much time on a complicated advanced solution that will probably be overhauled again.

[cbjeukendrup]

@zacjansheski Testing notes:

• the profile name in View > Playback Setup should be MuseSounds, not Muse Sounds
• all other occurrences of this renaming are handled not in this PR but in Remove space from "Muse Sounds" to "MuseSounds" in app #26969
• When opening a file from a previous version, the correct profile should still be selected when opening the file in this PR's build
• When adding new instruments to such a file, they should automatically load the correct sounds according to the selected profile

[zacjansheski]

Tested on MacOS 15, Windows 11, Ubuntu 22.04.3. Approved