Issue 3187: Ugly alignment of text and score within a markup

Issue 3187: Ugly alignment of text and score within a markup

For \score within \markup, the reference point (usually the middle
staff line) of the lowest staff in the top system is placed on the
baseline.

This is an incompatible change, but the previous behavior (placing the
_highest_ y coordinate of the score on the baseline, disregarding the
staves) was not useful.