merge: remove emptyactions() and use collections.defaultdict(list) instead emptyactions() used to return a dict which was populated and passed into applyupdates(). However, with recent changes, we no longer pass a plain dict, instead we pass the mergeresult object. There was only one usage of emptyactions and that too inside mergeresult object. That usage is replaced with collections.defaultdict(list) instead. Not sure why we were not using collections.defaultdict(list) from the beginning. Differential Revision: https://phab.mercurial-scm.org/D8903

merge: pass mergeresult obj in _forgetremoved() (API) Instead of returning a dict of actions and then updating it, let's pass the object directly and update it there. This makes `updateactions()` on mergeresult unused and this patch removes that. After this patch, we have couple of methods left on mergeresult class which still exposes the internal dict based action storage. Differential Revision: https://phab.mercurial-scm.org/D8889

mergeresult: introduce filemap() which yields filename based mapping We wanted to remove `actions` as this was leaking how we store things internally and was direct access to one of the member. This introduces filemap() which yields a map of `filename` -> `action, args, msg`. `mergeresult.actions` has been deleted as it's no longer required. Differential Revision: https://phab.mercurial-scm.org/D8888

mergeresult: add `files()` and use it `files()` will return a list of files on which an action needs to be performed. This is a step to stop exposing the underlying map to the user of this object. Differential Revision: https://phab.mercurial-scm.org/D8887

mergeresult: introduce getfile() and use it where required We want to hide the underlying dictionary from the users and provide API for valid and sane use cases. Differential Revision: https://phab.mercurial-scm.org/D8886

merge: use ACTION_* constants instead of values in _filternarrowactions() It makes easier to check what noconflicttypes are and which are not included. I hope we can have a state where we always use ACTION_* constants instead of these values which are very hard to understand. Differential Revision: https://phab.mercurial-scm.org/D8885