TAB: initial support for multiple voices.

Note fretting in one voice takes into account frets in other voices.
Stems, beams, etc are NOT adjusted yet.
fix arpeggio regression
fix too wide layout spacing
do not write control chars in XML
fix #18618 : File suffix has to be entered when saving snapshot
fix #13577 : Drag-selected lasso rectangle remains
fix #19129 : Small note in chord is detached from stem
fix bad alignment of small notehead in tablature
Fix #19931: Use native file dialog on windows and mac, and qt file dialog on unix
exclude more control chars from XML write
replace all subtype()/setSubtype() Element methods
new subType() Element method for selection gui
fix mtest
fix #20331 Attempting to move a measure number results in a crash
allow multi selection of same element type in inspector, part1
inspector updates
note inspector update
add missing files