The old flags used a size of 150x100, while the new assets based on
twemoji use a size of 150x108. Update existing usages to match this new
aspect ratio better.
Previously such use cases have been returning `null` values just fine since `GetLocalisableString` was returning `LocalisableFormattableString`, and these null values were wrapped in `LocalisableString`s implicitly, therefore not requiring an explicit fallback string and `null` doesn't break anything.
In theory this seemed like a good idea (and an optimisation in some
cases, due to lower fill rate), but in practice this leads to weird edge
cases.
This aims to do away with the operations on external drawables by
applying a dim to the area behind the `LoadingLayer` when required.
I went over each usage and ensured they look as good or better than
previously.
The specific bad usage here was the restoration of the colour on dispose
(if the `LoadingLayer` was disposed in a still-visible state).
I'm aware that the `BeatmapListingOverlay` will now dim completely during
load. I think this is fine for the time being.