Masked Clear Draw Changes:
- Use universal blendstate object
- Eliminate blendState cache for masked clears
- Use rasterState and scissor rect for scissoring instead of adjusting vertex positions
- VB contains only static position data (per vertex color removed)
- Clear color(s) and depth clear values now passed in using a constant buffer
- MultiColorclear shader used for float clears to workaround alpha rounding issues
- Update shader compile script and shader source and bytecode headers
- Remove unused shaders (source and bytecode headers)
- Use com pointers where possible for D3D11 objects

BUG=angleproject:1632

Change-Id: I98e38451bd453f53b772fe93ec9dcceb4196ea58
Reviewed-on: https://chromium-review.googlesource.com/413736Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Shahmeer Esmail <shahmeer.esmail@intel.com>
Commit-Queue: Jamie Madill <jmadill@chromium.org>