Improve diff lines count efficiency

This will help diagnose the source of excessive I/O from Rugged
calls. To implement this, we need to obtain the full list of arguments
sent to each request method.

This adds `rugged_duration_ms` and `rugged_calls` fields to
`api_json.log` and `production_json.log`. This will make it easier to
identify performance issues caused by excessive I/O.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/64676

When passing start_branch on committing from the WebIDE, it's possible
that the branch has changed since editing started, which results in the
change being applied on top of the latest commit in the branch and
overwriting the new changes.

By passing the start_sha instead we can make sure that the change is
applied on top of the commit which the user started editing from.

Igor Drozdov authored 5 years ago and Nick Thomas committed 5 years ago

This is part of migration of Folder View to Vue

Whenever we use the rugged implementation, we are going straight to disk
so we want to bypass the disk access check.

Suggests to use a JSON structured log instead

Related to https://gitlab.com/gitlab-org/gitlab-ce/issues/54102

Add a module we use as a singleton to determine whether or not rails is
able to access the disk

Currently, MergeToRefService is specifically designed for
createing merge commits from source branch and target branch of
merge reqeusts. We extend this behavior to source branch and any
target ref paths.