bug#57434: 28.1.91; Terminal Emacs Mac OS flickering.

[Eli Zaretskii]

> From: Dmitrii Kuragin <kuragin@google.com>
> Date: Wed, 7 Sep 2022 09:11:32 -0700
> Cc: Eli Zaretskii <eliz@gnu.org>, 57434@debbugs.gnu.org
> 
> Sorry I made you wait. I tried the patch (see attachments) and everything 
> worked perfectly. No flickering.

OK, thanks.

So now the next question is: on what should we base the activation of
these hooks?  There are several alternatives:

  . if alacritty produces a distinct value from tty-type, we could use
    that, or
  . if alacritty has a distinct terminfo capability that other
    terminals don't, we could use that, or
  . expose a variable to Lisp that users could set in order to turn
    this on and off, and tell users to turn it on if they see the
    issue

Any other ideas?

> BTW, tmux uses the sync update for their own TUI and they check "Sync" 
> terminal capability. Do we need to
> do the same or we can just send the escapes and hope the unsupported terminal 
> would just recover?

What is that Sync capability, what is its value for tmux, and how is
it supposed to be used?  Is there any documentation I could read about
that?