[thatbudakguy]

• Label polygons in index maps only once, at a sensible location
  This fixes a bug where some index maps would show the polygon
  labels repeated many times, because of the way that MapLibre picks
  locations to render text labels: it renders one for every disjoint
  polygon in a MultiPolygon, as well as every time a polygon crosses
  a tile boundary.

  This creates our own logic that picks the largest single part of
  a multipolygon to use as the host for a label for the group, so
  that index maps don't end up with crowded, duplicate labels.

• Make index maps render before PMTiles in tab order