Take advantage of the fact that all AST nodes now use an
`ast::Identifier` instead of directly using Symbols.
This will be important for ensuring that un-keyworded identifiers will
be preserved.
Bug: tint:1810
Change-Id: If5c3e9f00b4c1c14a6f11bd617bd8b895250fb7e
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/119285
Reviewed-by: Dan Sinclair <dsinclair@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Ben Clayton <bclayton@chromium.org>
4e4cada291