Remove store from Localhost client

[fedekunze]

Summary

Remove prefix store field from the localhost client and replace it with a cleaner approach.

Problem

The ICS09 localhost client requires to introspect the client store in order to verify state.

Nevertheless, the client needs to be stored in the state as well, so we end up storing the prefix store that is able to introspect itself.

cosmos-sdk/x/ibc/09-localhost/types/client_state.go

Lines 28 to 34 in e01a56e

	// ClientState requires (read-only) access to keys outside the client prefix.
	type ClientState struct {
	store sdk.KVStore
	ID string `json:"id" yaml:"id"`
	ChainID string `json:"chain_id" yaml:"chain_id"`
	Height int64 `json:"height" yaml:"height"`
	}

This is an antipattern and makes things very confusing.

Solution

Update the ClientState interface to pass an sdk.KVStore to all state verification functions.

cc: @AdityaSripal @cwgoes @colin-axner

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[cwgoes]

Yes, I think this approach is preferable (also see #6189 (comment)).