Teach ./bin/celerity about sprite maps

Summary:
Add ./bin/celerity sprites, to replace script ./scripts/celerity/generate_sprites.php.
Also make new workflow run ./bin/celerity map at the same time.

Fixes T15437.

Test Plan: Changes a file that goes in the sprites, run new command

Reviewers: O1 Blessed Committers, speck

Reviewed By: O1 Blessed Committers, speck

Subscribers: speck, tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Maniphest Tasks: T15437

Differential Revision: https://we.phorge.it/D25274