The Vulkan spec is being clarified to explain that the FragCoord passed
to a shader should use the unclamped depth value and that only the depth
test and depth write should use clamped values.

Bug: b/184063472
Change-Id: Ic76c13512745abea2181475eff5147134a1bf147
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/54668
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Tested-by: Sean Risser <srisser@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Commit-Queue: Sean Risser <srisser@google.com>