MINOR: filters: Support global instance sequencing

MINOR: filters: Support global instance sequencing

Accept global alongside request and response in filter-sequence. Global
constraints use the same class/instance references and loop checks, but
may order instances whose classes do not share a channel side. Moving a
instance in this order leaves its request and response positions alone.

Add native VTC coverage for global moves, inherited sequences and local
overrides. Reject self-references and cycles in all three orders, including
further lookups after a rejected move, with -conf-BAD instances for the
configuration diagnostics. CLI assertions are added with the inspection
commands in the next patch.