Allow the right-hand side of an 'in' expression to be of non-primitive object type.

Fixes #14269

Author: kpreisser

src/compiler/checker.ts

@@ -15546,7 +15546,7 @@ namespace ts {
             if (!(isTypeComparableTo(leftType, stringType) || isTypeOfKind(leftType, TypeFlags.NumberLike | TypeFlags.ESSymbol))) {
                 error(left, Diagnostics.The_left_hand_side_of_an_in_expression_must_be_of_type_any_string_number_or_symbol);
             }
-            if (!isTypeAnyOrAllConstituentTypesHaveKind(rightType, TypeFlags.Object | TypeFlags.TypeVariable)) {
+            if (!isTypeAnyOrAllConstituentTypesHaveKind(rightType, TypeFlags.Object | TypeFlags.TypeVariable | TypeFlags.NonPrimitive)) {
                 error(right, Diagnostics.The_right_hand_side_of_an_in_expression_must_be_of_type_any_an_object_type_or_a_type_parameter);
             }
             return booleanType;