Fix issue #23985.
Furthermore implements deleting all the measures covered by the multi-
fix #23011: change channel broken

Two separate bugs here.  First caused staff text channel changes to be
applied at the wrong time.  Second prevented channel changes to "normal"
from working at all.
fix tests

No longer save explicit "normal" channel name in imported scores.  Also
remove explicit "normal" channel name from Cymbal in instruments.xml.
update importmidi/updateReference script
missed two tests
fix #24349: fret offset text size as style
fix #24349: fret offset text left/right, as style
fix #24494: distance staff to fretboard diagram
minor fixes to the previous 2 commits

minor, as it works without those, but seems cleaner with:
ST_fretNumPos is int -> styleI() rather than stylD()
ST_staffFretDist gets multiplied by _spatium -> styleP() does this for
us, styleD() does not.
UI improvements
making fretboard distcance to staff consistent

with other similar settings by using negative values if above staff
fix chord symbol to fretboard diagram distance
fix #24657: save correct mixer info for instrument change
fix #24001: add "Text Style..." to context menu

open text style dialog, pre-set to text style of selected element
handle chord symbols
add simple MusicXML iotest to mtest
fix MusicXML vertical positioning
suppress "Text Style" in menu for unstyled text

Chord symbols treated as styled for this purpose, since the chord symbol
text style is always used.
Update instruments.xml

Change lowercase to upper for Mallet Synthesizer.
fix #24711: wrong chord height on 1.3 import

Scores that used the old default chord height (-4sp) were being loaded
using the new default chord height (0sp) and hence had chords much too
low.