[native] Fix pending state in ExistingEthereumAccount for identity auth

Summary:
Noticed while working on the stack ending in D11806 that the pending state here is only handled for the legacy auth.

Changed it here and did some corresponding reworking of the logic.

Depends on D11806

Test Plan: Careful reading of the code

Reviewers: inka

Reviewed By: inka

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D11807