Use the same API/pattern for parsing raster tiles as we use for vector
tiles. Forward the error as an exception that will ultimately reach the
StillImageCallback.
Also set the tile to State::obsolete on error like we do for vector
tiles.
Also add a virtual setState() method to give subclasses a chance
to intercept the change of state. This will be used by VectorTileData
to release resources when the TileData becomes immutable.
We are also removing the code that is passing the Environment around
and instead, we get now the Environment in the TileData using
Environment::Get().
When processing the job, the work will be temporally registered to
the Environment as "TileWorker_0/0/0" which can be used for logging
in the future. At the end of the job, it gets unregistered
automatically from the Environment.
we are now scoping all file requests to an environment object. The FileSource implementation treats
this as an opaque pointer, but allows canceling all Requests that are associated with that pointer.
This is necessary to abort all file requests that originated from a particular Map object. Aborting
a file request is different from canceling a file request: A canceled request doesn't have its
callback called, while an aborted request will have its callback called with an error, indicating
that the environment is going to be shut down.
