This is a bit of a hack, similar to how D3D11 works. We need to write
output locations in the GLSL shader before we send them to glslang,
so we wait until the link call, then string-replace some hard-coded
identifeir code to the attribute location determined by ANGLE.

This CL also fills in some of the vertex format conversion tables in
formatutilsvk.cpp.

BUG=angleproject:2167

Change-Id: I2424d0d990bdbcd831a4dd130e61e87d8f8f479f
Reviewed-on: https://chromium-review.googlesource.com/677555
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Frank Henigman <fjhenigman@chromium.org>