SymbolZElevate

Position symbol on buildings (both fill extrusions and models) rooftops. In order to have minimal impact on performance, this is supported only when fill-extrusion-height is not zoom-dependent and remains unchanged. For fading in buildings when zooming in, fill-extrusion-vertical-scale should be used and symbols would raise with building rooftops. Symbols are sorted by elevation, except in cases when viewport-y sorting or symbol-sort-key are applied.