Playback fixes for hairpin end dynamics

[Reedbeta]

Resolves: #31669

Playback would still use the hairpin's snapped end dynamic even if it had the "play" property unchecked. This PR adds checks for that property, so dynamics with "play" turned off are ignored; and also adds logic to search for a playable dynamic at the hairpin end point, if the one it's snapped to has "play" turned off.

This allows a setup like this, where the "ff" has play turned off, and the invisible "mf" has play enabled, to work as expected (the crescendo only goes to mf during playback).

To link up for playback, the end dynamic must be at the exact time tick where the hairpin ends, and must have the same voice assignment (i.e. same rules as snapping).

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[Reedbeta]

I found this assert failing if, while playback was running, I clicked in an empty area of the score (e.g. between staves).

[Jojo-Schmitz]

Rebase needed to fix the arm build