Due to the logic present to handle `@2x` fallback, the extension was
potentially being added at the wrong point in the filename. This change
ensures that the lookup filenames are always correct.
Closes https://github.com/ppy/osu/issues/17690.
Legacy skins should now always show the legacy hud components. The
conditional here is no longer valid as fallback lookups happen at a
*skin*-fallback level rather than internal *source*-fallback.
Put another way, `LegacyDefaultSkin` (with user customisations) should
still display the classic HUD components even if a font is not provided,
as that font will be available via the skin lookup hierarchy.
The TODO removed in this commit has been already resolved so this code
is no longer required.