Handle More Configurable Parts of CONFIG

[LukeAbby]

There is code like this:

  #createGroups(parentName, parent) {
    for ( const [name, config] of Object.entries(CONFIG.Canvas.groups) ) {
      if ( config.parent !== parentName ) continue;
      const group = new config.groupClass();
      Object.defineProperty(this, name, {value: group, writable: false});    // Reference on the Canvas
      Object.defineProperty(parent, name, {value: group, writable: false});  // Reference on the parent
      parent.addChild(group);
      this.#createGroups(name, group);                                       // Recursive
    }
  }

Which means everything under Config.Canvas.groups has profound effect on typing now, in a similar fashion to how Documents can be configured.

[JPMeehan]

Tied to #2572

[JPMeehan]

Also tied to #2593

[JPMeehan]

Thought: We move all of the layer definitions to an interface that Canvas extends, and then that interface can get some clean declaration merging.

[esheyw]

A shorthand for access to CONFIG.Canvas.rulerClass would be convenient to have