Initial focus in message compose screen

[cketti]

When opening the message compose screen, the focus should be on the first empty input field of "To", "Subject", and "Message text" (in that order).

This should do the right thing no matter what action lead to opening the message compose screen (compose, reply, forward, edit draft, mailto: URI)

See also #7618

[cketti]

@LorenzHo: For a proper fix I suggest extracting the initFromIntent() code to a separate (Kotlin) file in the com.fsck.k9.ui.compose package. Instead of calling methods on RecipientPresenter, AttachmentPresenter, etc., the code should return a data class containing the properties that have been extracted from the Intent. Then the calling code in MessageCompose will use the result to issue the appropriate calls to the presenters.

That should also allow us to write tests for the code to extract data from Intents.