Fix #15407: Hide zero-length lyrics dashes

[asattely]

Resolves: #15407
Resolves: #15093

See comment, the solution for this one has changed.

[asattely]

This one ended up being a little more in-depth than I expected it to be.

• If the user places exactly one underscore (or dash) and then ends editing, the melisma is deleted and the alignment of the lyric is reset.
• If the user places multiple dashes, the lyric will be left-justified (as it spans multiple notes), but if the editing ends with that string of dashes, the original lyric will again have its alignment reset and the "melisma" will be deleted.

[RomanPudashkin]

I would suggest moving it into navigate.h/cpp

[asattely]

I'm afraid I don't understand this one. You want the lyrics class to be in navigate.h?

[RomanPudashkin]

No, only this function :)

[asattely]

Issue #15093 was extremely similar, so I just added it to this PR since it deals with the same behavior.

If the ticks for a lyric become zero for any reason now (not just when editing a lyric finishes), the lyric re-lays-out to make sure invalid segments don't remain.

[RomanPudashkin]

This is not exactly what I meant :) You should declare a function in navigate.h (similar to prevChordRest):

extern Lyrics* prevLyrics(const Lyrics* lyrics);

Then use this new function in TextBase::endEdit(EditData& ed):

 if (isLyrics()) {
     Lyrics* prevLyrics = prevLyrics(toLyrics(this));
     if (prevLyrics) {
         ...
     }
 }

[asattely]

For the record, why do we want to do this? Is there a reason prevLyrics shouldn't be a method?

[RomanPudashkin]

Because it can iterate implicitly over the whole score. And in general, has low cohesion in this class (it does not depend on anything within this class, and can easily be moved out of it and take it as an argument). We want engraving elements to be as simple as possible