Addresses hover flicker from issues #5887 and #5506.
Also fixes issue #5475/#6298, so that symbols that bleed over tile boundaries don't get missed. Under the hood, there are some good simplifications:
 - No round-tripping of viewport query coordinates through tile space
 - No more need to merge duplicate results from the same symbol showing up in multiple tiles
 - All querying-related data can now be indexed with a bucket instance id and a feature index
 - `Placement` now manages lifetime of any data needed to query against its CollisionIndex
 - CollisionBoxArray no longer involved in querying at all

Tests issue #5475.

Matches topDownComparator of FeatureIndex.
Previous behavior was string sorting, which could provide unexpected results with multi-digit feature indices.
Update query tests to match new order.

…g symbols.

Fixes issue #6184.