merge: add removefile() to mergeresult object There are cases where some further calculation makes the file not needing to be merged anymore and hence needs to be dropped in mergeresult object. This adds a function for that. Differential Revision: https://phab.mercurial-scm.org/D8821

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

merge: improve documentation of fbid dict used for merge bid I improved the comments explaning what the dict contains meanwhile organizing the comment structure which prevents some confusion. Due to formatting issues, the empty dict was wrapped in `()` which might decieve in thinking that it's a tuple of dict until you decide to find a comma. Differential Revision: https://phab.mercurial-scm.org/D8818

merge: move conversion of file-key dict to action-key dict in mergeresult Initially the actions dict which we get has file has keys, but later we want a dict which has actions as keys. This patch moves code computing that to mergeresult class as that's where it should be anyway. Differential Revision: https://phab.mercurial-scm.org/D8817

merge: introduce hasconflicts() on mergeresult object This and upcoming patches will improve the mergeresult object making it more powerful and provide clean APIs for various things. Doing this will clean up the core merge code which is present in `update()` a bit. Differential Revision: https://phab.mercurial-scm.org/D8816