Ensure correct variant count in Runtime[Hold/Freeze]Reason (#1900)

closes https://github.com/paritytech/polkadot-sdk/issues/1882

## Breaking Changes

This PR introduces a new item to `pallet_balances::Config`:

```diff
trait Config {
++    type RuntimeFreezeReasons;
}
```

This value is only used to check it against `type MaxFreeze`. A similar
check has been added for `MaxHolds` against `RuntimeHoldReasons`, which
is already given to `pallet_balances`.

In all contexts, you should pass the real `RuntimeFreezeReasons`
generated by `construct_runtime` to `type RuntimeFreezeReasons`. Passing
`()` would also work, but it would imply that the runtime uses no
freezes at all.

---------

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

substrate/frame/balances/src/tests/mod.rs

@@ -27,7 +27,7 @@ use frame_support::{
 	parameter_types,
 	traits::{
 		fungible, ConstU32, ConstU64, ConstU8, Imbalance as ImbalanceT, OnUnbalanced,
-		StorageMapShim, StoredMap, WhitelistedStorageKeys,
+		StorageMapShim, StoredMap, VariantCount, WhitelistedStorageKeys,
 	},
 	weights::{IdentityFee, Weight},
 };
@@ -70,6 +70,10 @@ pub enum TestId {
 	Baz,
 }
 
+impl VariantCount for TestId {
+	const VARIANT_COUNT: u32 = 3;
+}
+
 frame_support::construct_runtime!(
 	pub struct Test
 	{
@@ -132,9 +136,10 @@ impl Config for Test {
 	type ReserveIdentifier = TestId;
 	type WeightInfo = ();
 	type RuntimeHoldReason = TestId;
+	type RuntimeFreezeReason = RuntimeFreezeReason;
 	type FreezeIdentifier = TestId;
 	type MaxFreezes = ConstU32<2>;
-	type MaxHolds = ConstU32<2>;
+	type MaxHolds = ConstU32<3>;
 }
 
 #[derive(Clone)]