Remove StructType::name()

This CL removes the name accessor from the StructType. All usages are
updated to use the symbol.

Change-Id: I65d793e9609a1663facce955bdb89e60f11f382a
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/36800
Reviewed-by: Ben Clayton <bclayton@google.com>

src/validator/validator_impl.cc

@@ -96,7 +96,7 @@ bool ValidatorImpl::ValidateConstructedTypes(
               add_error(member->source(), "v-0031",
                         "a struct containing a runtime-sized array "
                         "must be in the 'storage' storage class: '" +
-                            st->name() + "'");
+                            module_.SymbolToName(st->symbol()) + "'");
               return false;
             }
           }