There were cases in the editor where rewinding of transforms would
leave the `DrawableHitObject` in a non-`IsPresent` state, resulting in
this scheduled logic never running.
This would in turn cause ghost hitobjects, which disappear under certain
circumstances.
Reproduction:
- Open editor to empty beatmap
- Place single hitcircle at current point in time
- Drag editor timeline backwards to seek before zero, and wait for
return to zero
- Select hitcircle in playfield
- Drag hitcircle to right in timeline, triggering a start time change
This was firing regardless of whether the start time was changed, such
as where beat snap provided the same time the object already has.
The case where a change actually occurs is already handled by
EditorBeatmap (see `startTimeBindables`), so it turns out this local
handling is not required at all.
If the skin is changed before gameplay has started (at the loading
screen) it is possible for a sequence of events to occur which results
in the animation not being played:
- `SkinReloadableDrawable` runs its BDL load (and calls `OnSkinChanged`
once)
- User changes skin, triggering `DrawableJudgement`'s skin change
handling (binding directly on the `SkinSource` locally)
- This will call `PrepareDrawables` and reinitialise the
`SkinnableDrawable` child hierarchy, then immediately apply the
animations to it.
- The new `SkinnableDrawable` will then get the `SkinChanged` event and
schedule a handler for it, which will run on its first Update call.
- Any added animations will be lost as a result.
Fixed by binding directly to the `SkinnableDrawable`'s `OnSkinChanged`.
This has the added bonus of not needing to reinitialise the child
hierarchy on skin change (which felt a bit weird in the first place).
