merge: pass mergeresult obj instead of actions in _checkcollision() (API) The goal is to not use the actions dict and replace it with a rich mergeresult object. Differential Revision: https://phab.mercurial-scm.org/D8875

commitctx: directly update the touched and added set of files Instead of going through intermediate variable, we can simply use the ChangingFiles object. The object will take care of the consistency.

commitctx: directly updated the set of removed files The change is non-trivial so I made it in its own changeset.

commitctx: create the `ChangingFiles` object sooner Let us change the `_commit_manifest` call before other changes.

commitctx: move ChangingFiles creation directly inside `_process_files` As announced, we move it there. We focus on the signature change first, we will update the code afterward.

commitctx: create the ChangingFiles object directly in the various case No need to compute all data then create the object, we can create it early and directly store data in it. We start simple by moving create higher in the function, but the end goal is to eventually move the creation inside the `_process_files` function to take advantage of the object there.

commitctx: no longer make the storage and added/removed file optional The code using this variable is always using other, stricter, condition before using these value. So it is safe to always carry them along.

commitctx: directly gather p1 and p2 copies in `files` The only thing we do with the p1copies and p2copies is to pass them around, we we can gather them later and directly stored them in the `ChangingFiles` object.