ScrollbarStyles contains values of overflow, (over)scroll-behavior, etc.
The only one which is marginally related to scroll _bars_ is overflow, which can
be used to hide scrollbar (by making an element not scrollable) or enforce the
scrollbar to display.
It makes more sense to be called ScrollStyles as it's mainly concerning behavior
of scrolling, not scrollbars. Also, with the addition of scrollbar width
properties, the current name can be confusing.
Excludes layers/ipc/CompositorBridgeParent and CrossProcessCompositorBridgeParent
because the latter purposely uses functions implemented in the former.
See also code comment in CrossProcessCompositorBridgeParent.cpp
Note: likely dead code for us anyway; likely not worth investing in to solve.
This creates a number of stubs and leaves some surrounding code that may be irrelevant (eg. recorded time stamps, status variables).
Stub resolution/removal should be a follow-up to this.
