Add addNewAccountWithoutUpdate method

[rickycodes]

This adds a new method for adding accounts without updating identities in the preferences controller

this is currently being used in MetaMask/metamask-mobile#1879

[estebanmino]

LGTM!

[Gudahtt]

This approach would certainly work, but it is a departure from how the rest of the methods in this controller are designed. In the rest of the methods, all of the required "side-effects" of the action are handled as part of the same function. This controller was a port of various functions in the extension that are directly in metamask-controller.js that interact with the underlying eth-keyring-controller library that both projects use.

So to stay in line with existing patterns, the natural place to find and add new accounts would be during createVaultAndRestore, which is where it's done in the extension. So instead of adding this new method, you'd move this detect-and-add-accounts logic from MetaMask/metamask-mobile#1879 into this controller instead.

I don't feel strongly either way about this so I won't block on it, but because this was how it was done before I thought it should be considered.

[Gudahtt]

I see that createNewVaultAndRestore is used in a few places where new-account-detection would be undesired (e.g. upon changing your password), so maybe putting the logic there is less than ideal.

Maybe there should be two methods - createNewVaultAndRestore for this, and recreateVault for re-creating a vault with the same contents? 🤷 I think all of the uses are one of these two cases.

This might be a good idea for the extension as well 🤔