Fix #15726 (Glissando & Bends): Some elements are lost when changing time signature

[pacebes]

Resolves: #15726 (Glissando and Bends)

This PR keeps Glissando & Bends when changing time signature:

• TrackList read and write methods now clone Note's Spanners and rebuild Spanners End and Start elements

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[pacebes]

I have changed the way we clone Note's Spanners (outside Note copy constructor) to avoid failing tests.

There is a duplicated function (TrackList::cloneAndRebuildSpanners) and lamba function cloneAndRebuildSpannersWrite within write method) because write method is const ( bool write(Score*, const Fraction&) const; ). If we can change this method to "not const" (bool TrackList::write(Score* score, const Fraction& tick) ) we could avoid this duplication. I have not come up with any other way, any hint to avoid function duplication would be appreciated

[pacebes]

I have made some additional changes to simplify cloneAndRebuildSpanners function. I have also put it out of the class to avoid code duplication by allowing write method to use it.