[native] Consider BottomSheetHandle size when setting snapPoints

Summary: The height of BottomSheetHandle is always the same, and we should take it into account when setting snapPoints. More context here.

Test Plan: In combination with the rest of the stack, I tested each individual use of our BottomSheet component to make sure that the bottom padding was reasonable. In most cases it was unchanged; in other cases, it was changed to be more consistent with the other BottomSheets in our codebase. In all cases, there was enough padding for the "home pill" at the bottom of the screen

Reviewers: bartek

Reviewed By: bartek

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D13867