Implement `eth_decrypt` and `eth_getEncryptionPublicKey`. This allows decryption backed by the user's private key. The message decryption uses a confirmation flow similar to the messaging signing flow, where the message to be decrypted is also able to be decrypted inline for the user to read directly before confirming.
The `AccountDropdownMini` component featured the ability to switch
accounts using a dropdown, but this functionality was disabled in #6024.
It has been acting as a restyled `AccountListItem` since then.
The component has been removed, and the style changes moved to the sole
parent component (`RequestSignature`).