Fix #31176 - Appearing and disappearing courtesy clef

When courtesy clefs are turned off, some sequences of steps involving clef changes across system breaks result in spurious courtesy clefs being shown. Also, occasionally, the layout oscillates between showing / hiding courtesy clefs and/or fitting its measure in the same system or the next system. See http://musescore.org/en/node/31176 for details and examples.
Bar lines: fixing custom type and generated management

There are some inconsistencies in the current management of bar line `_generated` flag and user-modified type:

- Bar lines created by the New Score Wizard are flagged as non-generated, as well as bar lines of measures manually **appended** by the user, while bar lines of measures **inserted** are flagged as generated.
- If a generated bar line is individually changed of typed, it remains flagged as generated, it is not saved and the change is lost upon saving and re-loading.
- The management of the internal flag `BarLine::_customSubtype` is not always consistent.
- The `Measure::_endBarLineGenerated` flag was not always restored properly by undo.

This PR introduces the following fixes:

- The `_generated` flag is consistently used for bar lines whose type can be reconstructed from the context and then do not need to be saved to the output file.
- Normal bar lines are **always** created as generated: initially created by the Wizard, manually appended or inserted.
- Bar lines with custom type (i.e. different from the type which can be expected according to the bar line context) are always flagged as non-generated, ensuring the custom type is written to the output file.
- The `Measure::_endBarLineGenerated` flag is stored by `ChangeEndBarLineType()` and restore upon undo.
- Some test reference scores, based on the inconsistent bar line `_generated` flag, have been uniformed.

Notes:

- Tests about measure (and then bar line) appending, inserting and relative undo's are already included in the `tst_parts` test suite.
- Some inconsistencies remain in the management of custom bar line span and of system-initial bar lines: for the sake of simplicity, they will be dealt with in separate PR's.
fix #32116: [MusicXML] new-page on first measure shouldn't create one more page
fix #32356: Crash when pasting 'all' to new file
fix #31971: Staff names of hidden instruments appear
Merge pull request #1274 from mgavioli/Fix_31176_appearing_and_disappearing_courtesy_clef

Fix #31176 - Appearing and disappearing courtesy clef
Fix #32541 - Some artic. anchor not saved in style dlg

If some values are used for articulation anchors in the "Style | General" dlg box, they are not restored when opening the dlg again and presumably lost.

See http://musescore.org/en/node/32541 for details.
Add default value for BarLine::updateGenerated()
Merge pull request #1284 from mgavioli/Fix_32541_articulation_anchor_not_saved

Fix #32541 - Some artic. anchor not saved in style dlg
Merge pull request #1281 from mgavioli/barline_custom_type_and_generated

Bar lines: fixing custom type and generated management