fix(49478): add return type to method signature (#49482)

src/services/codefixes/helpers.ts

@@ -332,7 +332,7 @@ namespace ts.codefix {
                     /*questionToken*/ undefined,
                     typeParameters,
                     parameters,
-                    type
+                    type === undefined ? factory.createKeywordTypeNode(SyntaxKind.UnknownKeyword) : type
                 );
             case SyntaxKind.FunctionDeclaration:
                 return factory.createFunctionDeclaration(

src/services/textChanges.ts

@@ -682,7 +682,7 @@ namespace ts.textChanges {
             return {
                 indentation,
                 prefix: (insertLeadingComma ? "," : "") + this.newLineCharacter,
-                suffix: insertTrailingComma ? "," : ""
+                suffix: insertTrailingComma ? "," : isInterfaceDeclaration(node) && isEmpty ? ";" : ""
             };
         }