merge-actions: add some information about the "changes" the action do This will be useful when processing merges action outside of the narrow-spec. "support" outside of narrow file on commit Differential Revision: https://phab.mercurial-scm.org/D12118

merge-actions: have an attribute for narrow safetiness This allow the core doing narrow filtering to process action without explicitely listing all possible actions. This is important to make the actions system more flexible in the future. Differential Revision: https://phab.mercurial-scm.org/D12117