The Vulkan spec states that if an implementation does not support an
extension, then it must ignore all fields other than pNext and pType and
continue on without processing any further information contained in the
extension's structure. We've been using asserts to log these situations
so we can tell which extension structs people are trying to use.

This CL changes our behavior so we silently log these unsupported extensions,
and warn a user once if they're debugging.

Bug: b/139528538
Change-Id: I8d31f147e22f670c9c10c64e239085700eae73a3
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/36089
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Sean Risser <srisser@google.com>
Presubmit-Ready: Sean Risser <srisser@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>