shiny/driver/windriver: factor out a win32 package

A Windows version of the gldriver shares a lot of common code with
the existing windriver. This CL factors it out into a new internal
pacakge, win32.

For golang/go#9306

Change-Id: If602bb42946f1df662b2529d5b277257ae7706d3
Reviewed-on: https://go-review.googlesource.com/17676
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
9 files changed