If `merge_error` is ever set after a failure, it is never cleared, even
after a subsequent, successful rebase. We now clear this field whenever
a successful rebase occurs.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/56139

Sessions can be listed for a given user

See merge request gitlab-org/gitlab-ce!28306

Adds ActiveSession#session_ids_for_user for listing session IDs for a
given user, and adds ActiveSession#list_sessions for listing session
data directly.

Optimise upload path calls

See merge request gitlab-org/gitlab-ce!28264

String#underscore isn't particularly slow, but it's possible for us to
call it many times in a users autocomplete request, with mostly-static
values ('User', 'Group', etc.). We can memoise this and save a
surprising amount of time (around 10% of the total request time in some
cases).

Fix project visibility level validation

Closes #59379

See merge request gitlab-org/gitlab-ce!28305

Rename methods that conflict in Rails 5.2

Closes #55583

See merge request gitlab-org/gitlab-ce!28281

Resolve "Remove ignore_column ci_id"

Closes #61302

See merge request gitlab-org/gitlab-ce!28234

Adds suffix to enum methods and changes `in_groups` to
`of_groups`