val: Introduce debugMarker.spec.ts to test debug marker
val: Introduce debugMarker.spec.ts to test debug marker

This PR introduces a new debugMarker.spec.ts file in order to test
the validation of pushDebugGroup, popDebugGroup, and insertDebugMarker.

As a first test, this PR adds 'push_pop_call_count_unbalance' to
ensure that a validation error is generated if the {push,pop}
count is not paired.

Issue: #1928

gpuweb/cts,gpuweb/cts,gpuweb/cts