x/feegrant API audit

[blushi]

ref: #8983

• Are Msg and Query methods and types well-named and organized?
• Is everything well documented (inline godoc as well as /spec/ folder in module directory)
• Check the proto definition - make sure everything is in accordance to ADR-29

[aleem1314]

• proto definitions:

  • Proto definitions properly named as per the ADR-29.
  • Let's remove unused import cosmos/feegrant/v1beta1/query.proto:4:1: warning: Import gogoproto/gogo.proto is unused.
  • Few proto messages fields missing description FeeAllowanceGrant, QueryFeeAllowanceRequest, MsgGrantFeeAllowance, MsgRevokeFeeAllowance.

• specs & godocs

  • DeductGrantedFeeDecorator section is outdated, after refactoring ante handlers.
  • Same here.
  • In 03_events.md we can change section title: Handlers -> MsgServer.

• Msg & Query methods and types properly named

  • Msg & Query methods are properly named and well organized.
  • Few methods missing godoc in Msg & Query server.
  • QueryServer in keeper/grpc_query.go is not covered by unit tests.
  • Messages in types/msgs.go are not covered by unit tests.

[blushi]

Same as in x/authz, we should simplify msg and types naming.