fix #9004

A tile needs to be reparsed in order for it to use the new image.
Reloading all tiles whenever an image is added would be expensive. For
example:
- load a map
- add an image and use it in a geojson overlay

You don't want adding that image to make the basemap tiles be reloaded.

To get around that we track all the image ids used by each tile and only
reload tiles that depend on images that changed.