Implement getMultisamplefv for d3d part.Because standard D3D sample
positions from https://msdn.microsoft.com/en-us/library/windows/
desktop/ff476218.aspx are fixed sample pattern,we put the sample
positions into a constant array in renderer11_utils.cpp with a
function to query it.

BUG=angleproject:1590
TEST=dEQP-GLES31.functional.texture.multisample.samples_*.sample_position

Change-Id: I6e6006ed1c4e22fe006522e9ffd3297247bee75e
Reviewed-on: https://chromium-review.googlesource.com/594970
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>