Changed members filter state to preserve unknown NQL filter properties

[kevinansfield]

ref #28232

The multiple-active-subscriptions filter in #28232 needed to survive the members URL writeback, which was handled with a one-off preserveMultipleActiveSubscriptionsFilter mode bolted onto useMembersFilterState. That special case meant any other NQL the filter UI can't represent — unknown fields, OR groups, operators the field map doesn't advertise — was still silently scrubbed from the URL, breaking hand-crafted and legacy Ember filter links.

This generalises the underlying filter state handling so unknown NQL filter properties are always preserved, and removes the special-case mode entirely:

• The filter param is parsed once and split into its top-level AND clauses via the AST. Clauses that map to filter chips behave as before; every other valid clause is carried through the URL writeback, the nql output (so it still filters the member list via the API), and chip edits. Only "clear" actions remove them.
• Since nql-lang has no AST→string serializer, this adds one (serializeAstToNql) as the inverse of the parser for every shape its grammar can emit, including the ~/~^/~$ regex forms and preserved relative dates. It's deliberately conservative: anything it can't faithfully round-trip returns undefined and the clause is dropped rather than risk writing corrupted NQL back to the URL.
• When recombining clauses, root-level OR clauses are parenthesized (AND binds tighter than OR in NQL) so precedence survives the join.

The banner behaviour from #28232 is unchanged — it still exact-matches its filter in nql — but adding a chip on top of an unknown filter now ANDs the two together instead of dropping the unknown part, and unknown filters now work regardless of the labs flag (the flag only gates the banner UI).

Stacked on #28232 so only the refactor is in the diff; it'll retarget to main when that merges.

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