tint/ast: Generate ast::Extension from intrinsics.def

Emit unit tests for parsing and printing.
Emit benchmarks for parsing.
Uses intrinsics.def as a single-source-of-truth.
The generators provide a way to optimize the enum parsers.

Change-Id: I7f13128f510b2156c2ef724c89df7bb85dae17ed
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/97151
Commit-Queue: Ben Clayton <bclayton@chromium.org>
Reviewed-by: Dan Sinclair <dsinclair@chromium.org>

src/tint/sem/builtin.cc

@@ -164,9 +164,9 @@ bool Builtin::HasSideEffects() const {
 
 ast::Extension Builtin::RequiredExtension() const {
     if (IsDP4a()) {
-        return ast::Extension::kChromiumExperimentalDP4a;
+        return ast::Extension::kChromiumExperimentalDp4A;
     }
-    return ast::Extension::kNone;
+    return ast::Extension::kInvalid;
 }
 
 }  // namespace tint::sem