Enable custom transaction dialog for evm accounts

[tusharsoni]

Hey team,

We're building a snap for our MPC-based wallet that's gasless. This means, users don't require any ETH in their wallet to approve a transaction. Currently, the MM transaction window does not allow for a transaction to be approved if the wallet doesn't have gas in it.

For example, the following shows the transaction window blocking the transaction from going through (the Approve button is disabled). However, our service allows this transaction to go through as it's a gasless service.

Additionally, Metamask also does not allow for us to broadcast the transaction. This is important as we need to manage the nonce and broadcast it sequentially from our service.

Ideal Solution

1. Allow snaps to override certain UI elements in the transaction preview such as the gas estimation
2. Allow snaps to sign and broadcast the transaction. In this case, the snap would return the transaction hash back to the dapp.

Alternate Solution
Similar to the non-EVM accounts flow where Metamask allows a custom dialog to be presented for transaction review (see below), we should consider allowing the same for EVM accounts as well.

Custom dialog for Dogecoin transaction review