This struct will in the future hold information other than a length
resolution context (e.g. context for tree counting functions) and a
single struct is easier to work with than multiple parameters.
This reverts 0e3487b9ab.
Back when I made that change, I thought we could make our StyleValue
classes match the typed-om definitions directly. However, they have
different requirements. Typed-om types need to be mutable and GCed,
whereas StyleValues are immutable and ideally wouldn't require a JS VM.
While I was already making such a cataclysmic change, I've moved it into
the StyleValues directory, because it *not* being there has bothered me
for a long time. 😅
A cursor is an image, with an optional x,y hotspot.
We know that a CursorStyleValue's bitmap never needs to change size, so
we create the ShareableBitmap once and then cache it, so that we don't
have to repeatedly create an FD for it or do the work of painting.
To avoid repainting that bitmap, we cache the values that were used to
create it - what currentColor is and its length resolution context -
and only repaint when those change.
