sparse: replace merge action values with mergestate.ACTION_* constants Having bytestrings like `b'r'` makes it hard to understand for people who don't know the code much or looking at it for the first time. Differential Revision: https://phab.mercurial-scm.org/D8881

mergeresult: implement a len() function and use it In next patch we will start yielding from `getactions()` instead of building and returning a list. Hence we can no longer rely on that for getting us a length. Differential Revision: https://phab.mercurial-scm.org/D8880

merge: replace use of actions dict with mergeresult object There are still some places which can be improved by having a dedicated API, this patch for now make all users of actions dict go through the mergeresult object API. Differential Revision: https://phab.mercurial-scm.org/D8879

mergeresult: add sort argument to getactions() method This will be used in next patch. Differential Revision: https://phab.mercurial-scm.org/D8878

merge: pass mergeresult obj in merge._prefetchfiles() Differential Revision: https://phab.mercurial-scm.org/D8877

merge: pass mergeresult obj instead of actions in applyupdates() (API) This is similar to past 20 patches or so where we are replacing use of a bare actions dict with a dedicated mergeresult object. The goal is to have a dedicated powerful object instead of a dict while making the code more easier to understand. In past few patches, we have already simplified the code at some places using the newly introduced object. This patch does not updates applyupdates() to use the mergeresult object directly. That will be done in next patch to make things easier to review. Differential Revision: https://phab.mercurial-scm.org/D8876

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.

commitctx: extract sidedata encoding inside its own function This part of the code is quite independent from the rest. Thank to the new ChangingFiles object, moving with the rest of the sidedata code (in metadata.py) is simple. The changelog.add method is simply passing the `files` object to the new function. It will be easy to increase/change the data we gather and encode without impacting the changelog method.