map with any joblib backend

[lhoestq]

We recently enabled the (experimental) parallel backend switch for data download and extraction but not for map yet.

Right now we're using our iflatmap_unordered implementation for multiprocessing that uses a shared Queue to gather progress updates from the subprocesses and show a progress bar in the main process.

If a Queue implementation that would work on any joblib backend by leveraging the filesystem that is shared among workers, we can have iflatmap_unordered for joblib and therefore a map with any joblib backend with a progress bar !

Note that the Queue doesn't need to be that optimized though since we can choose a small frequency for progress updates (like 1 update per second).