merge: introduce mergeresult.addfile() and use it We want to use mergeresult object at more and more places instead of this actions dict to simplify code and further add new APIs to mergeresult object. This patch introduces `addfile()` which adds a new file to the internal actions dict for now. Differential Revision: https://phab.mercurial-scm.org/D8820

merge: make mergeresult constructor initialize empty object In future patches, we will be going to update mergeresult object instead of building an actions dict and then setting it in the object. Differential Revision: https://phab.mercurial-scm.org/D8819