While `EndTime + tickSpacing` _was_ closer to what stable was using, it
could cause undesirable edge cases wherein a tick would be spawned
outside of the drum roll's duration
(see https://github.com/ppy/osu/pull/23768/files#r1222073027).
For this reason, stick with the old code for now, as it is not as
susceptible to that sort of breakage.
`TestSceneEditorTestGameplay` is not isolated from database, and one of
the tests exiting editor when seeked to 60000 milliseconds
(`TestClockTimeTransferIsOneDirectional()`) ended up changing
`EditorTimestamp` to the same value, causing
`TestSaveChangesBeforeGameplayTest()` to fail due to changing initial
state.
To fix, perform a direct deletion of imported beatmaps in realm to avert
this scenario, contrary to the soft-deletion via `BeatmapManager` done
previously.
`dimensions` would always receive exactly one item, so might as well
inline it.
And yes, at this point the grid container is mostly a glorified
`FillFlowContainer { Direction = FlowDirection.Vertical }`, but I am not
touching that in this pull pending further decisions with respect to
direction.