Issue 4533: Stop the generic \tweak command from working as override

Issue 4533: Stop the generic \tweak command from working as override

The problem with letting the generic \tweak command work as an override
is that the tweaking of lyric events becomes awkward since plain lyrics
are hard to distinguish from property names.

This renames the combined tweak/override command into \propertyTweak and
changes all callers requiring the combined functionality to call
\propertyTweak (or its Scheme equivalent) rather than \tweak.

The original issue allowing \tweak to act as an override was issue 2929.
The issue allowing tweaks to function in \lyricmode is issue 2543.