The slight hack which was used in the test to ensure that the mod
settings overlay covered the entire width of the mod overlay broke after
adjustments to the layout in the previous commit.
Locally adjust the hack to use the parent of the `ModSettingsContainer`
rather than the container itself.
Uses the resolved working beatmap instead of resolving it every time.
Also uses the EditorBeatmap itself as playable beatmap, as it is of type `IBeatmap` already, and `.PlayableBeatmap` forwards everything anyway.
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`.