Unwrap NEAR on Aurora->NEAR transfers

[karim-en]

Description

NEAR instead of wNEAR on AuroraStoring native NEAR tokens on aurora account on NEAR - issues:

• This creates issues for accounting and monitoring - need to verify which part of aurora balance is used for storage, which is used for bridged NEAR, and which is free and available.
• Could create a lack of NEAR collateral for the bridged wNEAR - some users may not be able to withdraw their wNEAR from Aurora.

The solution:

• Keep holding wNEAR on aurora balance on NEAR side.
  • This way, each time the user bridges NEAR to Aurora, it's being wrapped to wNEAR and sent to Aurora.
  • We preserve the same ERC-20 address of wNEAR on Aurora without any additional steps.
• When withdrawing wNEAR from Aurora, make unwrap in wNEAR (call wrap.near near_withdraw()) and then send native NEAR tokens for users.
  • Use optional suffix {}:unwrap so it won't break the cross-chain swaps for Ref.Finance.

Implementation: Modify the ExitToNear precompile:

• Call near_withdraw instead of ft_transfer if the erc20_address is a wnear_address and the recipient end with the suffix {}:unwrap.
• Rename refund_on_error callback to exit_to_near_precompile_callback.
• Pass to it args with optional TransferNearCallArgs and an already existing RefundCallArgs but make it optional.
• In the exit_to_near_precompile_callback transfer near on successful promise result and refund on the failed result.

Performance / NEAR gas cost considerations

The gas consumption increased a little bit due to a callback call.

Testing

Integration tests are added

How should this be reviewed

The reviewer should focus on the changed components that are described in the implementation section, and verify that the implementation is backward compatible and doesn't break any other components like XCC and refund logic.

[joshuajbouw]

Why treat WNEAR differently than every other ERC-20 bridged token?

[sept-en]

@joshuajbouw this is because $NEAR is a native token in NEAR, and not NEP-141. So this change could allow users to create and/or top-up NEAR accounts easier and in more convenient way (it doesn't require a separate NEAR transaction and thus NEAR gas to unwrap wNEAR from the user).

Also, on NEAR->Aurora transfers of $NEAR we automatically wrap them so users receive wNEAR on Aurora. This PR will allow unwrapping on the way back.

[sept-en]

@karim-en could you please merge the latest changes from the develop branch?

[joshuajbouw]

Looks like CI is still failing.

[joshuajbouw]

Can you resolve conflicts please? Thanks.