devel/git: Split into subpackages

From: Renato Botelho <garga_at_FreeBSD.org>
Date: Fri, 08 Oct 2021 15:32:48 UTC
This idea was originally proposed by grembo@ [1] and I've been working 
on it since that.  I decided to add an extra subpackage, git-gui, 
because I believe it's useful.

New review [2] is available.  If nobody objects I plan to get it 
committed next week.

[1] https://reviews.freebsd.org/D30238
[2] https://reviews.freebsd.org/D32369
-- 
Renato Botelho