Implement Regions

[JPMeehan]

All files related to regions. Requires #2571 and many steps will involve #2572

• [ ] Core document implementation
  • [ ] Add resources/app/common/documents/region.mjs
  • [ ] Add resources/app/common/documents/region-behavior.mjs
  • [ ] Add resources/app/client/data/documents/region.js
  • [ ] Add resources/app/client/data/documents/region-behavior.js
• [ ] Secondary document updates
  • [ ] Update BaseScene
  • [ ] Update BaseToken
  • [ ] Update TokenDocument
• [ ] Applications
  • [ ] Add resources/app/client-esm/applications/sheets/region-behavior-config.mjs
  • [ ] Add resources/app/client-esm/applications/sheets/region-config.mjs
• [ ] Canvas Layers
  • [ ] Add resources/app/client/pixi/layers/placeables/regions.js
  • [ ] Add resources/app/client/pixi/placeables/region.js
• [ ] Shaders
  • [ ] Add resources/app/client/pixi/webgl/shaders/region/base.js
  • [ ] Add resources/app/client/pixi/webgl/shaders/region/adjust-darkness-level.js
  • [ ] Add resources/app/client/pixi/webgl/shaders/region/highlight.js