D3D11: Use built-in position for gl_FragCoord.z on SM 4.0+ If supported, used built-in pixel position input for the gl_FragCoord.z value. Exposed GL_EXT_clip_control only on feature level 10_0 or higher. Fixed: angleproject:347737886 Change-Id: I272ccce04cf6ad7921aa6cd5dc13f0de2f9ae561 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5679787 Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Alexey Knyazev <lexa.knyazev@gmail.com>