ast/hir: Rename field-related structures

StructField -> FieldDef ("field definition")
Field -> ExprField ("expression field", not "field expression")
FieldPat -> PatField ("pattern field", not "field pattern")

Also rename visiting and other methods working on them.

compiler/rustc_resolve/src/build_reduced_graph.rs

@@ -1426,19 +1426,19 @@ impl<'a, 'b> Visitor<'b> for BuildReducedGraphVisitor<'a, 'b> {
         }
     }
 
-    fn visit_field(&mut self, f: &'b ast::Field) {
+    fn visit_expr_field(&mut self, f: &'b ast::ExprField) {
         if f.is_placeholder {
             self.visit_invoc(f.id);
         } else {
-            visit::walk_field(self, f);
+            visit::walk_expr_field(self, f);
         }
     }
 
-    fn visit_field_pattern(&mut self, fp: &'b ast::FieldPat) {
+    fn visit_pat_field(&mut self, fp: &'b ast::PatField) {
         if fp.is_placeholder {
             self.visit_invoc(fp.id);
         } else {
-            visit::walk_field_pattern(self, fp);
+            visit::walk_pat_field(self, fp);
         }
     }
 
@@ -1458,13 +1458,13 @@ impl<'a, 'b> Visitor<'b> for BuildReducedGraphVisitor<'a, 'b> {
         }
     }
 
-    fn visit_struct_field(&mut self, sf: &'b ast::StructField) {
+    fn visit_field_def(&mut self, sf: &'b ast::FieldDef) {
         if sf.is_placeholder {
             self.visit_invoc(sf.id);
         } else {
             let vis = self.resolve_visibility(&sf.vis);
             self.r.visibilities.insert(self.r.local_def_id(sf.id), vis);
-            visit::walk_struct_field(self, sf);
+            visit::walk_field_def(self, sf);
         }
     }