Blender Git Loki

Fix T55589, T60967: Windows pen pressure issues at start/end of the stroke.

The new implementation uses WM_POINTERDOWN, WM_POINTERUP and WM_POINTERUPDATE
and the pointer API to process stylus events. This avoids the delays that comes
with the WM_MOUSE and WM_xBUTTON events. The implementation should work on
Windows 8, and Windows 10 with both legacy and new pen interaction.

It also changes how the pressure is reset when the Windows Ink implementation
is enabled. The previous version reset the pressure to full when the pen left
the screen, however for some hardware implementations this allowed a small
window where Blender may process the final move event and read the pressure
as full leaving a dot on the last event.

Differential Revision: https://developer.blender.org/D4314