Improve ACL tab performance by lazy fetching - #1660

Before we only made a copy if skipTranslate was true. This could
have cause errors with immutable arrays, so it is probably
better to copy everytime.

menuPlacement defaults to this anyway, no need to check
here again

By using useRef instead of createRef we can avoid
recreating the ref all the time.
Should result in a very, very minor performance boost.

Avoid potential rerenders for virtualized options
which can end up quite costly for larger lists.
Could also help with flickering and focus reset issues somewhat.

Previous code was just delaying the fetch by a second. It would still
fire all accumulated request anyway (e.g. requests for "C", "Co, "Cou",
"Cour", "Cours" and "Course", instead of just "Course".
Implements debouncing, which should make for less load
and cleaner rendering steps when searching in an async dropdown.

The 1s debounce delay predates the backend performance work on the ACL
role picker (see the opencast20-side fixes for /admin-ng/acl/roles.json):
when a search could take several seconds regardless, an extra second of
debounce was a small fraction of the total wait. Now that a real search
responds in roughly 100ms, the fixed 1s delay is the dominant, and now
clearly excessive, part of the perceived latency -- pull it down to 300ms,
in line with typical search-as-you-type debounce intervals, and give it a
name instead of a bare literal so it's easy to find and retune later.

The Access Policy tab (and the corresponding wizards) fetched every
role in the system (limit: -1) on open to populate each role dropdown
client-side. On instances with many thousands of roles this was a
multi-second, multi-megabyte request fired once per open.

fetchRolesWithTarget now accepts query/limit/offset/hasUser, and
AccessPolicyTable's role dropdowns search the backend as the user
types instead. The parent components only fetch a single role up
front, just to read the isSanitize flag that decides whether users
and non-user roles are split into separate tables.

DropDown gains a loadOptionsOnMount flag so a fetchOptions-based
dropdown can skip its eager default-option fetch on mount (used here
since AccessPolicyTable renders one dropdown per existing policy row,
which would otherwise fire one identical request per row on tab open)
and instead fetch its default option list lazily, the first time that
particular instance is opened. This also fixes the virtualized
MenuList silently rendering nothing instead of react-select's
no-options/loading message when there are no options yet.