Generating hash of call data

[rajdeep7Singh]

This issue is a request to get support for generating call hash with call data.

Context: Few calls in Multisig Pallet in substrate based chains expects call hash as argument and some expect call data. For ex multsig.approve_as_multi and multisig.as_multi. When indexed we have no way to relate those txns without generating a call hash with call data in whatever call that is missing.

If possible can we have it injected into calls so we don't have to do it in our squids?

Providing reference how js apps is achieving that: https://github.com/polkadot-js/apps/blob/master/packages/page-preimages/src/Preimages/Add/Partial.tsx#L45