Fixed Mouse Under WindowsDX

This PR fixes the mouse behavior to work like XNA as described in https://github.com/mono/MonoGame/issues/2464.

Fixes bug introduced in https://github.com/mono/MonoGame/pull/2644.

Fixes https://github.com/mono/MonoGame/issues/2748.
I tried adding Application.Idle +=  but since I'm using WPF with a WinForm Host control, it doesn't seem to ever happen.