Remove duplicated tab for main score & enable setMovable (to allow reordering of parts)
Since #8954: Move Tabs Around has been fixed, I would now like to allow user to reorder each parts tab by clicking and dragging on them.
However, we cannot simply make the parts tab movable, because that would allow user to move a part before the main score, and unfortunately Qt does not have an easy way to prohibit a particular tab from being reordered. But I've proposed an alternative workable solution to remove the main score tab from the secondary tab, like:
in which case pressing on a Parent Score tab on top would display the main score in the scoreView, and would also deselect any selected tab for child tab using setCurrentIndex(-1).
Note to implementer: if have split view, will need to keep child scores tabs synced, like I did with https://github.com/musescore/MuseScore/commit/dd7fbe26571dc0c157c6c3847…