upgrade: split definition and management of the actions from the main code...
upgrade: split definition and management of the actions from the main code
This is a second step to clarify and clean up this code. The code responsible
for definition which action exist, are possible and their compatibility if moved
into a sub module.
This clarify the main code and prepare further cleanup.
Differential Revision:
https://phab.mercurial-scm.org/D9477