Fix #300340: Additive Time Signatures Do Not Appear Properly in the G…

[elerouxx]

…onville Font

Resolves: https://musescore.org/en/node/300340

Fixes a series of problems with spacing in which a sequence of glyphs is drawn as a string, and in particular, the 'advance' space value that was set to zero in case of a fallback glyph.
This includes sequence of time signature glyphs in certain fonts including Goinville, some sequences of glyphs that build mordents and ornaments, and some problems with dynamics with more than one glyph (ppp, fff).

For horizontal spacing:
_Found a call to ScoreFont::advance() that pointed to an override version that didn't compute the advance value from the fallbackFont. Because of this, the missing + glyph was drawn from the fallbackFont but its advance was set to zero.

For vertical spacing (when stretching the time signature):
_Found a call to ScoreFont::BBox() that pointed to an override version that didn't allow scaling in different horizontal and vertical dimensions.

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[elerouxx]

This vtest fail is actually a fix too. Looking closely to that mordent in musejazz

. In the reference render, the second half of the mordent slightly overlaps the middle vertical line (almost imperceptible).
As seen in detail (before/after):