- Added a loop for handling pNext pointers everywhere in
  libVulkan.cpp where the wasn't already one, in order to
  always output the unsupported structure type(s) received
  by the library
- Changed UNIMPLEMENTED to WARN for unhandled pNext pointers

Fixes the test:
dEQP-VK.api.smoke.triangle_ext_structs

Bug: b/144999059 b/119321052
Change-Id: Id83b5e74c8925dbd38651747b0cea46fac4a69a4
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/38548
Presubmit-Ready: Alexis Hétu <sugoi@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Sean Risser <srisser@google.com>
Reviewed-by: Chris Forbes <chrisforbes@google.com>
Tested-by: Alexis Hétu <sugoi@google.com>