Add Graphics to the Match3 env (#4627)
* first pass - matching and gravity work
* valid moves WIP
* move enumeration, simple checking
* move detection
* fix up/down directions
* actuator and heuristic
* sensor
* reset if no moves
* add masking, retrain
* cleanup
* config update
* optionally force heuristic mode
* compressed observations, reset board if no moves
* TFModel meta files
* WIP abstract
* random move heuristic
* rename Move fields, migrate IsValid logic
* comments
* reduce dependency on Match3Agent
* abstractBoard as monobehavior
* move actuator to extensions
* move sensor to extensions
* update components in scene
* undo accidental checkins
* drawing cleanup, custom maxMoves logic
* meta file
* prefab, use 8 agents
* different behaviors
* timers, early out
* unit tests
* docs
* Apply suggestions from code review
Co-authored-by: Vincent-Pierre BERGES <vincentpierre@unity3d.com>...