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 allows us to use the same method of checking for other files that should exist, for example the audio file.
By using the same method, they all share test cases too.
Makes use of the new `BeatmapSet.GetPathForFile` method and removes dependency on `WorkingBeatmap` specifically, allowing us to switch to `IWorkingBeatmap` later.
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.
Making those always non-null is postponed as when a replay's frame contains keypress the behavior is changed.
Previously, the key is pressed at the time of the first frame. But using non-null frames means the key is pressed at negative infinity.
However, I think the new way of always using non-null frames makes the client code so I plan to bundle the change to more breaking changes.
This is a workaround of a timing issue.
KeyCounter is disabled while break time (`HasCompleted == true`).
When the last keypress is exactly at the same time the map ends, the last frame was considered in a break time while forward play but considered not in a break time while rewinding. This inconsistency made the last keypress not decremented in the key counter when a replay is rewound.
The situation regularly happens in osu!standard because the map ends right after the player hits the last hit circle. It was caught by `TestSceneGameplayRewinding`.
This commit makes the update of the map completion delayed one frame. The problematic keypress frame is now processed strictly before the map completion, and the map completion status is correctly rewound before the keypress frame.
