Notes:
- INSTANTIATE_TEST_CASE_P is now deprecated, so changed it to
  INSTANTIATE_TEST_SUITE_P. This requires and update to
  third_party/googletest.
- Updated Driver's loadSwiftShader() function to include the
  non standalone path, in order to run the tests in Chromium
- Added Vulkan unit tests to swiftshader_tests
- Added a new GN file for Vulkan unit tests. Note that it
  relies on Chromium's version of SPIR-V Tools, not on
  SwiftShader's version, in order to avoid build conflicts

Change-Id: I87727f6a858a720d0f5fb8f262ac290818945ac4
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/32349
Presubmit-Ready: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Alexis Hétu <sugoi@google.com>