Use bitflags to compress function properties

Very minor savings, only 1 MB or so

crates/hir_ty/src/method_resolution.rs

@@ -675,7 +675,7 @@ fn is_valid_candidate(
                 }
             }
             if let Some(receiver_ty) = receiver_ty {
-                if !data.has_self_param {
+                if !data.has_self_param() {
                     return false;
                 }
                 let transformed_receiver_ty = match transform_receiver_ty(db, m, self_ty) {