Add regression test

Author: ahejlsberg

tests/cases/conformance/types/keyof/keyofAndIndexedAccess.ts

@@ -354,4 +354,15 @@ interface Options2<Data, Computed> {
 declare class Component2<Data, Computed> {
     constructor(options: Options2<Data, Computed>);
     get<K extends keyof Data | keyof Computed>(key: K): (Data & Computed)[K];
+}
+
+// Repro from #12641
+
+interface R {
+    p: number;
+}
+
+function f<K extends keyof R>(p: K) {
+    let a: any;
+    a[p].add;  // any
 }