The 10g Intel/Win driver doesn't work well with our emulated
intermediate mode. This patch alters the drawing of the drag widget of
the panels to reduce unneeded drawing.
The previous method would draw 16 boxes per widget. This new way would
cache this drawing in a GPU batch and just move the matrix around.
Reviewed By: Clément Foucault
Differential Revision: https://developer.blender.org/D7345
60d873bd22