Rename TypeRef -> Type

The TypeRef name comes from IntelliJ days, where you often have both
type *syntax* as well as *semantical* representation of types in
scope. And naming both Type is confusing.

In rust-analyzer however, we use ast types as `ast::Type`, and have
many more semantic counterparts to ast types, so avoiding name clash
here is just confusing.

xtask/src/codegen/gen_syntax.rs

@@ -476,7 +476,13 @@ impl Field {
                 };
                 format_ident!("{}_token", name)
             }
-            Field::Node { name, .. } => format_ident!("{}", name),
+            Field::Node { name, .. } => {
+                if name == "type" {
+                    format_ident!("ty")
+                } else {
+                    format_ident!("{}", name)
+                }
+            }
         }
     }
     fn ty(&self) -> proc_macro2::Ident {