The clip distance is used to perform per-fragment clipping - any fragments with a negative linear-interpolated distance are discarded.

The cull distance is used to perform per-primitive culling - any primitives with all vertices with a negative distance are discarded.

Bug: b/139207336
Tests: dEQP-VK.clipping.*
Change-Id: Ia6680601b27599152f68410df47aaaa726d0b349
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/34915
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Ben Clayton <bclayton@google.com>
Reviewed-by: Chris Forbes <chrisforbes@google.com>