Loading spinner for osmtogeojson operation

Currently, the map loading spinner goes away when the data is received from the OSM API. But it still takes a bit more time before the data is rendered on the map. Let's show the loading spinner until the data has arrived on the map.

Trace the map loading spinner from the OSM API response through the osmtogeojson operation and map rendering path. Confirm the spinner currently ends on data receipt, then verify it remains visible until the data has arrived on the map and disappears afterward.

Written by the indexing model from the issue text.