Fixes #5576

This allows contracts to be used with an AccountId32 through normal
extrinsics and not only through the eth compat layer. It works by adding
a new extrinsic `map_account` that lets people register their
AccountId32.

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Co-authored-by: command-bot <>
Co-authored-by: GitHub Action <action@github.com>
Co-authored-by: Cyrill Leutwiler <cyrill@parity.io>