Trim and fade for the wave part

[maiko3tattun]

New Features:

• Trim Wave Part: Not only UVoicePart but also UWavePart can now be trimmed.
• Fade: Grab the control at the edge of the Wave Part to set the fade.

Tested items:

• Limits on part trimming
• Limits on part fading
• Display in light mode and dark mode
• Voice part trimming isn't broken
• File saving and restoration
• Undo and Redo (There is a minor bug where the view occasionally fails to update during redo operations)