[Mobile Account Snaps] Migrate all accounts references to selectors about metamask-mobile

[gantunesr]

From a discussion with @owencraston,

1. Replace all direct calls to the preferences-controller state (selectedAddress or identities) to either a selector or the useAccounts hook depending on the case. This should be also a good opportunity to add unit test in critical parts if they're missing.
2. Resolve the inconsistency regarding importTime between the data type in the accounts-controller and preferences-controller. The easiest option is to use the preferences-controller data. Important to take into consideration a similar approach as extension of blocking the user of adding duplicated accounts
3. Change the preference-controller selectors to accounts-controller selectors (selectSelectedAddress or selectIdentities).

Considerations,

• Keep in mind the InternalAccountStruct against the Identity type