Also add a bunch of tests.

Bug: b/126028338
Change-Id: Ic8eb822dce3eff402e2a5f222c5077c6831f4505
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/25748Tested-by: Ben Clayton <bclayton@google.com>
Presubmit-Ready: Ben Clayton <bclayton@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>