Support public and private key encryption

[RyanDinh8]

Is your feature request related to a problem? Please describe.

Support asymmetric encryption/decryption feature on SubWallet

Sumi Network (wallet-to-wallet communication solution - https://www.sumi.network/) is asking SubWallet to support them in terms of public and private key encryption.

• Sumi Network demo at Decoded 2022: https://www.youtube.com/watch?v=a8P5xHkMqzI

Solution for Substrate accounts:

• Solution in this PR to support encrypt/decrypt functions on Polkadot JS
  • Why this PR is not accepted?
  • Security concerns of this PR
  • How to make this PR get passed?

Solution for EVM accounts

Documentations from MetaMask:

• https://docs.metamask.io/guide/rpc-api.html#eth-decrypt
• https://docs.metamask.io/guide/rpc-api.html#eth-getencryptionpublickey
• Example on (https://metamask.github.io/test-dapp/)
• Why these methods will be deprecated on MetaMask
  • https://medium.com/metamask/metamask-api-method-deprecation-2b0564a84686
  • Few users?
  • Security?
• Security concerns of these methods
• Follow MetaMask

More information:

• https://docs.metamask.io/guide/rpc-api.html#unrestricted-methods
• https://docs.metamask.io/guide/signing-data.html#a-brief-history

[S2kael]

The reason Metamask deprecated encrypt/decrypt functions on their Extension (Video).

[sondotpin]

https://github.com/polkadot-js/common/blob/9e3b42b32e2823fae3590a9c65350b6a08396e54/packages/keyring/src/pair/index.spec.ts#L182

encrypt/decrypt using sr25519 has supported via this PR