Fix circular dependency between BatchHandler and the renderer index

[pavle-goloskokovic]

This PR

• Fixes a bug

Describe the changes below:

BatchHandler requires the whole renderer index just to read two event names from Renderer.Events. Since the renderer index also (indirectly) requires the render nodes, this is a circular dependency, and whether it breaks depends on which side loads first.

The existing builds happen to load the renderer index first, so they are fine. A custom build that loads core/Game first reaches BatchHandler through RenderNodeManager before the index. BatchHandler then pulls in the index, which loads BatchHandlerQuad, which extends a BatchHandler that is still an empty object. The game fails at startup with "TypeError: Object prototype may only be an Object or null: undefined".

Fix: require renderer/events directly, as WebGLRenderer, WebGLPipeline and RenderTarget already do. No behaviour change for the existing builds.