* Introduce new Runtime API endpoint
`persisted_validation_data_with_code_hash` that will be used
by the candidate validation subsystem in order to decrease amount
of runtime API requests.
* Node-side part of new runtime API request
* Define code hash getter via macro
* Rename new endpoint to `assumed_validation_data`
* Docs for runtime API impl of new endpoint
* AssumedValidationData specialized request function
* fmt