[Perf] Improve texture loading

[jailln]

Context

From Don McCurdy's blog:
By default, three.js decompresses images and uploads them to the GPU the first time the image is rendered in the scene. To upload the image sooner, use WebGLRenderer's .initTexture() method. Using ImageBitmapLoader can take the decompression step off the main thread, reducing dropped frames somewhat.

Preload textures around currently loaded tiles when queue is empty (https://threejs.org/docs/?q=renderer#api/en/renderers/WebGLRenderer.initTexture et https://threejs.org/docs/?q=imagebit#api/en/loaders/ImageBitmapLoader)

Description of the proposal

Texture fetching and loading to the GPU could be improved by:

• using ImageBitmapLoader when available to take the decompression step off the main thread. Beware that it is not always supported, see the following condition
• Preloading textures to the GPU when the queue is empty (WebGLRenderer.initTexture)