This was not spotted previously, because the base `Attribute` overrides
`Equals()` to have semantics similar to structs (per-field equality) by
using reflection. That masked the issue when strings were used, and
migrating to `LocalisableString` revealed it, as that struct's
implementation of equality currently uses instance checks.
Whether `LocalisableString.Equals()` is the correct implementation may
still be up for discussion, but allowing multiple enumeration is wrong
anyway, since the underlying enumerables are live (one especially is a
yield iterator, causing new object instances to be allocated).
By moving this to a central location, we can avoid invoking the
EditorChangeHandler when there is no selection made. This helps
alleviate the issue pointed out in
https://github.com/ppy/osu/issues/11901, but not fix it completely.
This only covers constant rate rate adjust mods. Mods like wind up/wind
down will need a more complex implementation which we haven't really
planned yet.
Due to the use of bindable flow provided by `BeatmapDifficultyCache` in
this usage, the display would briefly flash to zero while difficulty
calculation was still running (as there is no way for a consumer of the
provided bindable to know whether the returned 0 is an actual 0 SR or a
"pending" calculation).
While I hope to fix this by making the bindable flow return nullable
values, I think this particular use case works better with non-bindable
flow so have switched across to that.