pallet-multisig: Improve opaque call handling (#10060)

* pallet-multisig: Improve opaque call handling

Before the opaque call was just a type redefinition of `Vec<u8>`. With metadata v14 that was
breaking external tools, as they stopped looking at the type name. To improve the situation the
`WrapperKeepOpaque` type is introduced that communicates to the outside the correct type info.

* Cleanup

* Fix benchmarks

* FMT

substrate/frame/support/src/traits.rs

@@ -52,7 +52,8 @@ mod misc;
 pub use misc::{
 	Backing, ConstU32, EnsureInherentsAreFirst, EstimateCallFee, ExecuteBlock, ExtrinsicCall, Get,
 	GetBacking, GetDefault, HandleLifetime, IsSubType, IsType, Len, OffchainWorker,
-	OnKilledAccount, OnNewAccount, SameOrOther, Time, TryDrop, UnixTime, WrapperOpaque,
+	OnKilledAccount, OnNewAccount, SameOrOther, Time, TryDrop, UnixTime, WrapperKeepOpaque,
+	WrapperOpaque,
 };
 
 mod stored_map;