devel/talloc242: Hierarchical pool based memory allocator

A hierarchical pool based memory allocator with destructors. It uses
reference counting to determine when memory should be freed.

This port is needed for Samba 4.20

This commit is just a repocopy. I will update the port to the correct
version and connect it to the build in the next commit.

PR: 280533
Sponsored by: Klara, Inc.
Approved by: 0mp (mentor)
Approved by: samba (0mp, kiwi)
Differential Revision: https://reviews.freebsd.org/D48657