Clean up structs for Rect and LParam/WParam with X/Y values

[dremin]

May want to look at creating an LParam struct type that can be tested. We can either have methods for grabbing int or intptr or implicit operators.

Good point, I will look into adding this. While working on this I noticed the RECT struct we have is being misused in some places, which threw me off for a bit, so I will clean that up too.

See: https://github.com/cairoshell/ManagedShell/issues/58#issuecomment-1087774176_