Mail · Writing: the composer, recipients that suggest, a signature, send later

MailComposer writes a message: To, and Cc and Bcc once asked for, as
tag fields that suggest contacts and mark what is not an address; the
subject and the words; the files, each with a way off; the signature
under the words. Send wakes once there is someone to send to and every
address is one; it hands over the draft now or at a time, and Discard
lets it go. A new start from the owner begins the draft over.

forms::TagInput now suggests: the rows that hold the typed words float
under it through the list Combobox uses; Up, Down and Enter pick, and
Escape sets them aside. RecipientInput points to it. ScheduleSend
offers tomorrow morning, tomorrow afternoon, Monday morning, or a day
and hour picked in a dialog. SignatureEditor writes the lines and shows
how they sit under a message; it tells the owner's echo from a new
signature, so the caret stays.

src/forms/tests/mod.rs

@@ -3,6 +3,7 @@ mod colors;
 mod dates;
 mod other;
 mod structure;
+mod tags;
 mod upload;
 
 use gpui::{