Split `definitions/document.ts` into unique files per actor type.
Create `model` folder to store the above types, their factories and the state changing actions.
* Create cache for blended layers to speed up rendering on Documents with blended content
* Manage blend mode caching state through layer changes in Document canvas
* Comments updated
* Moving files around
* Omit invisible layers in snapshot rendering
* Add pausing to blend layer cache
* Cleanups and tests for LayerSprite
* Remove logs
* Use actual LayerSprite in test
* Simplify pending check
* Omit flush calls on (un)pausing of cache
* Extend tests for LayerSprite
* Update modifier key tooltip
* Create reusable function for invalidating blend cache
* Updated tests
* Allow partial cache flushes
* Ensure blended layer cache is flushed appropriately on undo
* Pause blend caching while rotating or scaling
* Fix for Safari rendering issues
