base: tube: allow to clone sending part of the tube
base: tube: allow to clone sending part of the tube

After commit c286772db82ba38a207981aa8b17d0c4ecb628fe the directional
Tube was intruded:
- SendTube which is clonable
- RecvTube which is not
Above was introduce to achieve MPSC and the original Tube::try_clone become
deprecated (preventing to create multi-producer, multi-consumer
communication channel).

In some scenarios cloning Tube only for sending purpose is needed and
doesn't break MPSC assumption since receiving is only allowed on
original Tube. To achieve above the Tube::try_clone_send_tube is
introduced.

BUG=None
TEST=Build

Change-Id: I1290904e5ccdccfc37c88e06655e585eda4a680f
Reviewed-on: https://chromium-review.googlesource.com/c/crosvm/crosvm/+/4011819
Commit-Queue: Grzegorz Jaszczyk <c5b88449c8a12e1c1d01de50f0c2b638f2b76073@google.com>
Reviewed-by: Noah Gold <2d4550d8af93bfc6e6fbe1fb1b0cc97a9ee7c3ce@google.com>
Reviewed-by: Daniel Verkamp <72bc170b46ec491f7bdd4359a1c0bfed274de40c@chromium.org>

google/crosvm,google/crosvm,google/crosvm,google/crosvm