This implements `hover`, `pointer`, `any-hover` and `any-pointer` and
the values `course`/`fine` (pointer) and `hover`.
A best effort is made to get capabilities from the system but if unknown
always falls back to assuming a mouse is present.
Microsoft IME on Windows 10 20H1 (build 19025+) supports IME private
mode by input scope. Although previous Windows versions use an
undocumented API for Edge and IE only, the next Windows 10 release will
use a public API for it.
We pre-empt this potential privacy concern by setting the IS_PRIVATE
flag when in PB mode.