uncommit: enable support for adding a note
This comes from the evolve extension's version of uncommit. The logic was
already in place, and appears to be the last of the trivial things that can be
enabled.
Should these note options (including on amend) be marked advanced to keep the
help text clutter level down?
Differential Revision: https://phab.mercurial-scm.org/D6857
[workspace]
members = ["hg-core", "hg-direct-ffi", "hg-cpython"]
exclude = ["chg", "hgcli"]