TextScript, CombineTextScript: use aligned_on_parent

I think this makes more sense than just using "self-alignment".
It makes these grobs consistent with Lyrics and Dynamics, and
allows users to override their alignment more predictably.

Expected changes in output: TextScripts and CombineTextScripts
will be aligned slightly different when the user sets self-alignment-X
explicitly (parent notehead will be included in alignment, as in Lyrics).
Default placement should remain the same.

I'm also changing one regtest, just to make sure that despite slightly
changed alignment the markups will stick out far enough to the left.