Every cell at exactly level that intersects a rectangle.
S2's coverer treats a minimum level as non-negotiable and will happily return
millions of cells rather than truncate, so callers driving this from a camera
should go through coverRectangle and its budget instead.
Every cell at exactly
levelthat intersects a rectangle.S2's coverer treats a minimum level as non-negotiable and will happily return millions of cells rather than truncate, so callers driving this from a camera should go through coverRectangle and its budget instead.