refactor: x/evidence as a standalone go module

[kocubinski]

Ref: #11899

The SDK module dependency graph below (generated from main 2023-01-09) shows that x/evidence has no dependents. Given this it should be trivial to create a go.mod for this module and separate it from the SDK monolith.

x/evidence has dependencies on the SDK modules shown below. As a part of this issue lets do a cursory review and remove them if trivial, or punt to the dependency's issue if not.

$ goFmtString="{{ \$importPath := .ImportPath }} {{ \$forTest := .ForTest }}                                                               
{{ range .Imports }} {{ if \$forTest }} {{ \$forTest }}.test {{else}} {{ \$importPath }} {{end}}-> {{ . }}
{{ end }}"
$ go list -test -f "$goFmtString" ./... | awk -F'->' '$2 ~ "github.com/cosmos/cosmos-sdk/x/"' | awk -F'->' '$2 !~ "github.com/cosmos/cosmos-sdk/x/evidence"'
  github.com/cosmos/cosmos-sdk/x/evidence/keeper -> github.com/cosmos/cosmos-sdk/x/staking/types
  github.com/cosmos/cosmos-sdk/x/evidence/testutil -> github.com/cosmos/cosmos-sdk/x/auth
  github.com/cosmos/cosmos-sdk/x/evidence/testutil -> github.com/cosmos/cosmos-sdk/x/auth/tx/config
  github.com/cosmos/cosmos-sdk/x/evidence/testutil -> github.com/cosmos/cosmos-sdk/x/auth/types
  github.com/cosmos/cosmos-sdk/x/evidence/testutil -> github.com/cosmos/cosmos-sdk/x/bank
  github.com/cosmos/cosmos-sdk/x/evidence/testutil -> github.com/cosmos/cosmos-sdk/x/bank/types
  github.com/cosmos/cosmos-sdk/x/evidence/testutil -> github.com/cosmos/cosmos-sdk/x/consensus
  github.com/cosmos/cosmos-sdk/x/evidence/testutil -> github.com/cosmos/cosmos-sdk/x/consensus/types
  github.com/cosmos/cosmos-sdk/x/evidence/testutil -> github.com/cosmos/cosmos-sdk/x/genutil
  github.com/cosmos/cosmos-sdk/x/evidence/testutil -> github.com/cosmos/cosmos-sdk/x/genutil/types
  github.com/cosmos/cosmos-sdk/x/evidence/testutil -> github.com/cosmos/cosmos-sdk/x/mint/types
  github.com/cosmos/cosmos-sdk/x/evidence/testutil -> github.com/cosmos/cosmos-sdk/x/params
  github.com/cosmos/cosmos-sdk/x/evidence/testutil -> github.com/cosmos/cosmos-sdk/x/params/types
  github.com/cosmos/cosmos-sdk/x/evidence/testutil -> github.com/cosmos/cosmos-sdk/x/slashing
  github.com/cosmos/cosmos-sdk/x/evidence/testutil -> github.com/cosmos/cosmos-sdk/x/slashing/types
  github.com/cosmos/cosmos-sdk/x/evidence/testutil -> github.com/cosmos/cosmos-sdk/x/staking
  github.com/cosmos/cosmos-sdk/x/evidence/testutil -> github.com/cosmos/cosmos-sdk/x/staking/types
  github.com/cosmos/cosmos-sdk/x/evidence/types -> github.com/cosmos/cosmos-sdk/x/authz/codec
  github.com/cosmos/cosmos-sdk/x/evidence/types -> github.com/cosmos/cosmos-sdk/x/gov/codec
  github.com/cosmos/cosmos-sdk/x/evidence/types -> github.com/cosmos/cosmos-sdk/x/group/codec
  github.com/cosmos/cosmos-sdk/x/evidence/types -> github.com/cosmos/cosmos-sdk/x/staking/types

List of To-dos when creating a go.mod: https://github.com/cosmos/cosmos-sdk/blob/main/CONTRIBUTING.md#gomod