D3D: Move some HLSL-specific code to a new folder. This code doesn't actually call any D3D runtime methods, so it can be included in our cross platform unit tests. Just include the varying packing code for now. BUG=angleproject:1296 BUG=angleproject:1638 Change-Id: I5c0ccccb00e1c13ca98448256be048f7cd0968ce Reviewed-on: https://chromium-review.googlesource.com/417116 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org>