These are two examples of a top-level `before` block doing too much.
Only specific specs cared about these guest users, but we were creating
them and their `ProjectMember` records for every single spec that ran.

Change `logout_direct` uses to `gitlab_sign_out_direct`

Change single `login_via` use to `gitlab_sign_in_via`

Fix https://gitlab.com/gitlab-org/gitlab-ce/issues/27070

Deprecate "chat commands" in favor of "slash commands"

We looked for things like:

 - `slash commmand`
 - `slash_command`
 - `slash-command`
 - `SlashCommand`

Remove slash commands from Markdown preview and display their outcome next to
the text field.
Introduce new "explanation" block to our slash commands DSL.
Introduce optional "parse_params" block to slash commands DSL that allows to
process a parameter before it is passed to "explanation" or "command" blocks.
Pass path for previewing Markdown as "data" attribute instead of setting
a variable on "window".

Removed all the unnecessary include of `WaitForAjax` and `ApiHelpers` in the specs.
Removed unnecessary usage of `api:true`

merge_request_for_resolving_discussions ->
merge_request_to_resolve_discussions_of

And deduplicate the finding of MR's & discussions. Now the searching
is done in the service, istead of the controller & the API.

Delegate a discussion in a merge request into a new issue.
The discussion wil be marked as resolved and a system note will be
added linking to the newly created issue.

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