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 #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.
fix tests, added new test

the new test is just a basic chord symbol compatibility test, which we
needed anyhow
When adding and instrument to a score with a pickup bar (anacrusis), set the displayed duration to the pickup length and not a full measure rest
Merge pull request #701 from lvinken/musicxml-fixes-2

Musicxml fixes 2
Merge pull request #702 from chenlung/master

Change lowercase to upper for Mallet Synthesizer
Merge pull request #703 from MarcSabatella/24711-chord-height-read114

fix #24711: wrong chord height on 1.3 import
Merge pull request #700 from MarcSabatella/24001-text-style-context

fix #24001: add "Text Style" to context menu
some more tests for text
change escape seq. for symbols in text