Merge pull request #21947 from Microsoft/fixKeyofWildcard

Fix issue with 'keyof T' and conditional types

src/compiler/checker.ts

@@ -7949,6 +7949,7 @@ namespace ts {
         function getIndexType(type: Type): Type {
             return maybeTypeOfKind(type, TypeFlags.InstantiableNonPrimitive) ? getIndexTypeForGenericType(<InstantiableType | UnionOrIntersectionType>type) :
                 getObjectFlags(type) & ObjectFlags.Mapped ? getConstraintTypeFromMappedType(<MappedType>type) :
+                type === wildcardType ? wildcardType :
                 type.flags & TypeFlags.Any || getIndexInfoOfType(type, IndexKind.String) ? stringType :
                 getLiteralTypeFromPropertyNames(type);
         }