ADR 003: Handler implementation (informalsystems#197)

* Add doc comments and error types to ICS 02 module

* Rename ics02_client::client module to ics02_client::raw

* Replace message traits with structs

* Fix formatting error

* Add implementation specific error kind

* Fixup client message structs definitions

* Fix clippy warnings

* Add basic handler definitions

* Add initial implementation of CreateClient handler

* Add implementation of ClientDef for Tendermint

* Re-use existing traits

* Add valid test for create_client handler

* Add tests for case where client already exists

* WIP: Update client handler

* Add initial proposal for ADR 003

* Rename file to adr-003-handler-implementation.md

* Replace "handler" with "message processor" in plain text

* Formatting

* Fix create client handler tests

* Rename module handler to dispatch

* Formatting

* Add sketch of update client processor

* Move mocks into their own module

* Remove genericity over client def in client submodule

* Lift chain specific data into an enum

* Update ADR to match new handling of chain-specific data

* Fix the connection specifics in ADR

* Added Tendermint to the new "Any*" enums

Added client state to MsgCreateAnyClient, result, keeper, etc

Test for concrete tendermint MsgCreateClient

Updated TM client and consensus states, MsgCreateClient

Extract client and consensus states from MsgCreateClient for TM

Extract consensus state from MsgUpdateClient for TM

Co-authored-by: Adi Seredinschi <[email protected]>
Co-authored-by: Anca Zamfir <[email protected]>