[tint][wgsl] Move LanguageFeature to a separate target

This target is special in that the GN build is entirely dependency-free.

This is to allow the target to be used outside of Dawn, and Chromium can
inspect the allowed features without having to create a Dawn device via
the wire.

Change-Id: I85ddfd76b897ae582fbffb734b4760872844190d
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/163320
Auto-Submit: Ben Clayton <bclayton@google.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
diff --git a/src/tint/lang/core/attribute_test.cc b/src/tint/lang/core/attribute_test.cc
index ac6b338..10d8e72 100644
--- a/src/tint/lang/core/attribute_test.cc
+++ b/src/tint/lang/core/attribute_test.cc
@@ -146,7 +146,7 @@
 TEST_P(AttributePrintTest, Print) {
     Attribute value = GetParam().value;
     const char* expect = GetParam().string;
-    EXPECT_EQ(expect, tint::ToString(value));
+    EXPECT_EQ(expect, ToString(value));
 }
 
 INSTANTIATE_TEST_SUITE_P(ValidCases, AttributePrintTest, testing::ValuesIn(kValidCases));