Add ValidFailInEnum

See kaitai-io/kaitai_struct#435 (comment)

formats/valid_fail_in_enum.ksy

@@ -0,0 +1,13 @@
+meta:
+  id: valid_fail_in_enum
+  endian: le
+seq:
+  - id: foo
+    type: u4
+    enum: animal
+    valid: # there is actually 7 in the file
+      in-enum: true
+enums:
+  animal:
+    4: dog
+    12: chicken

spec/ks/valid_fail_in_enum.kst

@@ -0,0 +1,11 @@
+id: valid_fail_in_enum
+data: enum_0.bin
+# NOTE: `s4` is not correct here. It should be the `valid_fail_in_enum::animal`
+# enum. However, if we specified it as
+# `ValidationNotInEnumError<valid_fail_in_enum::animal>`, KSC would think it's a
+# user-defined type and throw an error, because such user type doesn't exist.
+#
+# The type argument is only relevant to C++, though, so we pass `s4` here just
+# to pass something and the generated C++ test specs will have to be fixed
+# manually.
+exception: ValidationNotInEnumError<s4>