Check for depthBounds support in shader builtin frag depth tests

Check for depthBounds support in shader builtin frag depth tests

Depth bounds testing was enabled without checking for feature support
in a couple of tests. With this change, tests that don't need this
feature leave it disabled, whereas other tests (currently only
dEQP-VK.glsl.builtin_var.fragdepth.*) now throw NotSupported when
the device doesn't support it.

Affects:

dEQP-VK.clipping.*
dEQP-VK.glsl.builtin_var.*

Components: Vulkan

VK-GL-CTS issue: 685

Change-Id: I44d94142e295ff135ad1a55d0d6e212b65994257