[tint] Use explicitly (small) sized enums

Reduces memory usage of these enums.

Change-Id: Id04602611168bf6836ec7e2f99d4a651574d5ccc
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/145542
Commit-Queue: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: James Price <jrprice@google.com>
diff --git a/src/tint/lang/wgsl/writer/ast_printer/ast_printer.h b/src/tint/lang/wgsl/writer/ast_printer/ast_printer.h
index c84fa13..525b683 100644
--- a/src/tint/lang/wgsl/writer/ast_printer/ast_printer.h
+++ b/src/tint/lang/wgsl/writer/ast_printer/ast_printer.h
@@ -67,7 +67,7 @@
 }  // namespace tint::ast
 
 namespace tint::core {
-enum class TexelFormat;
+enum class TexelFormat : uint8_t;
 }  // namespace tint::core
 
 namespace tint::wgsl::writer {