Roll VK Headers/Loader/ValidationLayers forward.
There's a build improvement as well as many new checks.

Added new source file dep, convert_to_renderpass2.cpp, used by core_
validation for added RenderPass2 checks.

Also had to move glslang fwd for shader validation layer so updated
from confusing upstream branch of glslang that's integrated with shaderc
to the independent Khronos glslang repo.

Bug: angleproject:2937
Bug: chromium:845519
Change-Id: Ifee911f061dc426404c09499e49c2f029b174d03
Reviewed-on: https://chromium-review.googlesource.com/c/1355508Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Tobin Ehlis <tobine@google.com>