Use special classes when is_compare, similar to is_commit. Default
expectation is diff is being viewed in MR

Signed-off-by: Rémy Coutable <remy@rymai.me>

Add spec file using before(:context) to reduce test time. With testing
almost identical things, unnecessary to make them completely atomic.
Includes two helper methods. Since the raw_content method is the only
function needed on that page, created the method in the spec instead
of adding another page object.

Setup new project/commit page object and update project/show to add
go_to_commit method. The go_to_commit method is near duplicate of
go_to_file method, but decided to split them off to reduce overall
refactoring and simplify language.

Also add selectors to commit box partial and update qa.rb to load
new page object.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/54503

Rename btn-new, btn-create and btn-save to btn-success

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

The status is shown for
- The author of a commit when viewing a commit
- Notes on a commit (regular/diff)
- The user that triggered a pipeline when viewing a pipeline
- The author of a merge request when viewing a merge request
- The author of notes on a merge request (regular/diff)
- The author of an issue when viewing an issue
- The author of notes on an issue
- The author of a snippet when viewing a snippet
- The author of notes on a snippet
- A user's profile page
- The list of members of a group/user

Resolve "Commits page tooltips"

Closes #29278

See merge request gitlab-org/gitlab-ce!20674