test-runner: Consider wgsl output as validated

The resolver is the closest thing to a validator in this case.
Enables `--generate-expected` for WGSL files that were previously marked as SKIP.

Change-Id: Id7979ec39571ff52a2beb4255d88e4eb0962b82a
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/54650
Auto-Submit: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: James Price <jrprice@google.com>
Reviewed-by: James Price <jrprice@google.com>

tools/src/cmd/test-runner/main.go

@@ -400,6 +400,8 @@ func (j job) run(wd, exe, dxcPath, xcrunPath string, generateExpected, generateS
 		// Can we validate?
 		validate := false
 		switch j.format {
+		case wgsl:
+			validate = true
 		case spvasm:
 			args = append(args, "--validate") // spirv-val is statically linked, always available
 			validate = true