Also split out validation tests from call_test.cc into call_validation_test.cc.
Bug: tint:886
Change-Id: I1e1dee9b7c348363e89080cdecd3119cc004658f
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/54063
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: David Neto <dneto@google.com>