Add ability to view and adjust velocity and samples from the timeline

[peppy]

• Depends on Move DifficultyControlPoints to be specified at a per-HitObject level #14619
• Closes Add the ability to change slider velocity from compose mode #7882

Changing samples:

Changing velocity from popover:

Changing velocity from end shift+drag:

Tracking one issue with a test still, but wanted to get this PR out so it can be used to test the dependent PR #14619.

[smoogipoo]

Really need to be able to undo the changes, is that possible to be done in this PR?

[peppy]

If it's not already working all signs point to "probably not" (it's already using the correct update paths such that it should work if it can), but I'll take a look.

[bdach]

Relatively certain that having undo work with this requires #10314 for control points at least, because the beatmap patcher ignores everything but [HitObjects] sections, and so undo/redo doesn't work with the timing tab on master as is.

[peppy]

Undo isn't going to happen in this pull request.

[smoogipoo]

Sample volume propagation doesn't work on sliders (needs to propagate to the slider head). Sliders also behave weirdly when shift+dragged really fast: https://drive.google.com/file/d/1k0MTa_a3h3ktlqVrfGaQ76JaGilRAFGY/view?usp=sharing

Can merge as is and fix these up in a separate PR if you want.

[peppy]

Weird, I'll try and fix the dragging one.

[peppy]

@smoogipoo can you test the dragging again? i haven't 100% fixed the underlying issue, but a early-return equality check has stopped it happening for me, so should be in a good state to get merged at least.

[smoogipoo]

Still happens :( Maybe you can schedule + cancel this to fix? Though we intended to not throw random schedules around...