Add support for [[builtin(workgroup_id)]]

This is a trivial mapping to/from WGSL in all cases.

Bug: tint:478
Change-Id: I7f21a2392543a880906b54fddbdb8bbd149a526e
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/48140
Commit-Queue: James Price <jrprice@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
Auto-Submit: James Price <jrprice@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>

src/reader/spirv/enum_converter.cc

@@ -86,6 +86,8 @@ ast::Builtin EnumConverter::ToBuiltin(SpvBuiltIn b) {
       return ast::Builtin::kLocalInvocationIndex;
     case SpvBuiltInGlobalInvocationId:
       return ast::Builtin::kGlobalInvocationId;
+    case SpvBuiltInWorkgroupId:
+      return ast::Builtin::kWorkgroupId;
     case SpvBuiltInSampleId:
       return ast::Builtin::kSampleIndex;
     case SpvBuiltInSampleMask:

src/reader/spirv/enum_converter_test.cc

@@ -217,6 +217,7 @@ INSTANTIATE_TEST_SUITE_P(
                     ast::Builtin::kLocalInvocationIndex},
         BuiltinCase{SpvBuiltInGlobalInvocationId, true,
                     ast::Builtin::kGlobalInvocationId},
+        BuiltinCase{SpvBuiltInWorkgroupId, true, ast::Builtin::kWorkgroupId},
         BuiltinCase{SpvBuiltInSampleId, true, ast::Builtin::kSampleIndex},
         BuiltinCase{SpvBuiltInSampleMask, true, ast::Builtin::kSampleMask}));
 

src/reader/wgsl/parser_impl.cc

@@ -85,6 +85,9 @@ ast::Builtin ident_to_builtin(const std::string& str) {
   if (str == "global_invocation_id") {
     return ast::Builtin::kGlobalInvocationId;
   }
+  if (str == "workgroup_id") {
+    return ast::Builtin::kWorkgroupId;
+  }
   if (str == "sample_index") {
     return ast::Builtin::kSampleIndex;
   }

src/reader/wgsl/parser_impl_variable_decoration_test.cc

@@ -121,6 +121,7 @@ INSTANTIATE_TEST_SUITE_P(
         BuiltinData{"local_invocation_index",
                     ast::Builtin::kLocalInvocationIndex},
         BuiltinData{"global_invocation_id", ast::Builtin::kGlobalInvocationId},
+        BuiltinData{"workgroup_id", ast::Builtin::kWorkgroupId},
         BuiltinData{"sample_index", ast::Builtin::kSampleIndex},
         BuiltinData{"sample_mask", ast::Builtin::kSampleMask},
         BuiltinData{"sample_mask_in", ast::Builtin::kSampleMaskIn},