When TINT_BUILD_WGSL_WRITER is enabled.
This allows printing of the AST for debugging purposes.
Change-Id: I92b5911c16cb1e5fd22e81def00de33e9257f575
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/78541
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: James Price <jrprice@google.com>