Swing text: playback lost

See https://github.com/musescore/MuseScore/pull/4171

Fixed in branch master, commit c74eb802b4

fix #277648: try to distinguish between StaffText and SystemText on 2.X import

Initial issue is about swing playback which was imported as staff
text and hence did not apply to all staves. The fix tries to handle
system-wideness properly by looking at the style name of the text.
It is better to retrieve an actual value of "system flag" property
for the given style but it is unclear currently whether it is possible
to do so.

Concerning compared style names:
"Tempo" is the style name for the swing text in the original issue
"System" is the style name for system text elements
Other names are put just by assumption based on which elements in
MuseScore 3 are system-wide by default.

Fixed in branch master, commit 5e214c41a9

Merge pull request #4171 from dmitrio95/277648-swing-2X-import

fix #277648: try to distinguish between StaffText and SystemText on 2.X import

I've merged the PR which fixes the issue. MTest including midi check could be added for this case.

and that's why it is stil active rather than fixed?

@Jojo yep. Just not to forget about the issue.

The issue itself is fixed, but regression tests to prevent it from coming back are not yet added