Implements count-in, playing 'tick-tack' each time playback is started.

Ticks are always played for at least one full measure. If the playback starting point is not at the beginning of a measure or if the measure is shorter than nominal (anacrusis), also plays enough 'tick-tack' to fill the measure.

Count-in is turned on / off with a button in the play panel.
fix #22128: slurs in guitar pro
fix #23188: hairpin extends to end of score on copy/paste or save/reload
any spanner breaks multi measure rest
fix #23163
fix #23140
update mtest
edit slurs: change anchor while dragging
attach new local help system
Merge pull request #504 from mgavioli/count_in

Implements count-in, playing 'tick-tack' each time playback is started.
synchronize loop marker with pianoroll
fix #23219 (spelling errors)
fix #23191
fix #23145
fix editing of bar number in staff != 0
Rename makeLyricsList -> makeLyricsListForUI
Rename setInitialIndexes -> assignLyricsToTracks
Rename setLyrics -> setLyricsToScore
Add lyrics of tracks with notes to common lyrics list

(not only special lyrics from lyric tracks in karaoke files)
Reduce length of each lyric fragment (in the UI lyrics list) to 16 symbols