Create EmailForm component extracted from UpdateEmail for reuse

What does this MR do and why?

Allow verification code to be sent to any of a ... (#416451 - closed) will allow a user to enter a verified secondary email associated to their locked account where they will receive a new verification code. In preparation for that, this MR extracts the email form component from UpdateEmail¹ so it can be reused (see !165313 (merged)).

There are no behavior changes introduced in this MR. Existing behavior is covered by a feature spec.

¹Component that handles one-time email update.

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