Map move invalidates queryRenderedSymbols coordinates until next placement

Nobody has claimed this yet.

From https://github.com/mapbox/mapbox-gl-js/pull/6497#issuecomment-380910858:

`queryRenderedSymbols` is always based on the size/location of symbols at the time the last placement/collision detection completed. This means that when the map is changing, the results will tend to be a little stale (symbols with `*-allow-overlap: true` may be rendered on screen but not show up in the collision index, symbols may be rendered at larger/smaller size than recorded in the index, etc.). Having some delay in when items show up or disappear from query results is not ideal, but we think it's usually not too big a deal.

There's another problem, though: if you change the position of the map, the same viewport coordinates will map to different lat/lon values. So, if you query a recently moved map, you won't get stale results from the same lat/lon -- you'll get stale results from the _viewport coordinate_, which now has a different lat/lon. This has the potential to be pretty confusing: imagine an interactive feature that uses flyTo animations in combination with some sort of hover effect. If the user brought their cursor over the map while it was animating, the hover effect would work as if their cursor were at a random offset from its actual location (depending on how long it had been since the last placement).

Fixing the "stale results" problem entirely is hard, but I think we should be able to do a decent job of keeping coordinates in sync. At the time we call `queryRenderedSymbols`, instead of just using the current viewport query coordinates, we should use the current transform to convert the viewport coordinates to lat/lon, then use the last placement's transform to convert back into the viewport coordinates that would have obtained when the last placement ran.

/cc @ansis

Start at the queryRenderedSymbols entry point and trace how the current viewport coordinates and the last placement transform are used. Reproduce the issue while moving the map during a flyTo animation, then verify that query coordinates are converted through the current and last-placement transforms so results stay aligned with the same lat/lon.

Written by the indexing model from the issue text.