When searching for issues within a project or group, `IssuableFinder`
has an optimization that uses a CTE to filter the list of authorized
issues before searching within the list for text. This CTE optimization
fence is currently only used when the user specifies a simple sorting
parameter, such as `created_at`, and not popularity. These attributes
are generally stored directly with the model, so the CTE can easily do
an `ORDER BY` without joining another table (e.g. `award_emoji` for
popularity).

This commit adds the remaining simple sort attributes (due date,
relative position) the `Issue` class. This should help speed up the
search query and avoid a database statement timeout.

Improves https://gitlab.com/gitlab-org/gitlab/issues/34661