Port ComputeIndirectValidationTests to WGSL

Bug: dawn:572
Change-Id: I0db11c2416ca430b026cd2293061e99d35b18973
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/33924
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Ben Clayton <bclayton@google.com>

src/tests/unittests/validation/ComputeIndirectValidationTests.cpp

@@ -22,11 +22,8 @@ class ComputeIndirectValidationTest : public ValidationTest {
     void SetUp() override {
         ValidationTest::SetUp();
 
-        wgpu::ShaderModule computeModule =
+        wgpu::ShaderModule computeModule = utils::CreateShaderModuleFromWGSL(device, R"(
-            utils::CreateShaderModule(device, utils::SingleShaderStage::Compute, R"(
+            [[stage(compute), workgroup_size(1)]] fn main() -> void {
-                #version 450
-                layout(local_size_x = 1) in;
-                void main() {
             })");
 
         // Set up compute pipeline