Move PointerId, focus and in-bounds handling down into Interactivity (#20017)

These do not notionally belong to TermControl; as we prepare to move
automatic scrolling down into the Interactivity layer (for
WpfTerminalControl to depend on,) we're going to need to track these in
Interactivity too.

This also converts the arguments from the winrt-specific
Foundation::Point to Core::Point, and simplifies some of the signatures
to no longer pass things we do not need to pass.

Right now, this should result in no functional change.

Some of the tests are sensitive to the fact that we never loaded
`SPI_GETWHEELSCROLLLINES`
and instead defaulted to `1`. They've been hammered back into shape.