Add regression test

Author: ahejlsberg

tests/cases/compiler/mappedToToIndexSignatureInference.ts

@@ -1,3 +1,11 @@
 declare const fn: <K extends string, V>(object: { [Key in K]: V }) => object;
 declare const a: { [index: string]: number };
 fn(a);
+
+// Repro from #30218
+
+declare function enumValues<K extends string, V extends string>(e: Record<K, V>): V[];
+
+enum E { A = 'foo', B = 'bar' }
+
+let x: E[] = enumValues(E);