R1:cb938d869c3f

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.