`MainCirclePiece` specifies a state transform starting at
`StateUpdateTime`, which is earlier than the previously-used
`HitStateUpdateTime`. Change the transform clearing logic to use the
former to ensure that exactly all animation transforms are cleared.
Until now, the implementation of the overrides in `SelectionBlueprint`
have been confusing to the point where I would just implement by
trial-and-error (or copying from an existing implementation). This was
due to a combination of using "object" space coordinates
(ie. the thing the `Blueprint` is operating on) and screen-space coordinates.
This change switches all event related coordinates to screen-space,
which is how we already handle rotation/scale operations. With the
introduction of other editor types where the related objects are
drawables, this also makes a lot more sense.
This is different from the working beatmap's `.Beatmap` property in that it is mutated by the ruleset/editor.
So hit objects, for example, are actually of type `Slider` and such instead of the legacy `ConvertSlider`.
This should be preferred over `workingBeatmap.Beatmap`.
This lets us access things like the background, track, etc. which are necessary for quality and filesize checks.
Also improves the structure of the `CheckBackgroundTest` class in the process.