Use RenderTarget properties to reduce manual render state tracking

[mrxz]

The PackedSplats and Readback classes kept track of various properties of the render state in order to restore them afterwards. The WebGLRenderTarget has properties for scissor/scissorTest which, when used, cause the WebGLRenderer to keep track of and restore them for us when switching render targets. This simplifies the code as there is less state to track and no longer a need to adjust the pixelRatio (as this doesn't apply to render targets).

I've also changed the xrPresenting to xrEnabled, since the isPresenting flag is considered readonly in Three.js (WebXRManager.js#L100-L107). Temporarily disabling the WebXR code paths in the renderer should be done by setting xr.enabled to false, as can also be seen in the Reflector for example (Reflector.js#L201).

[dmarcos]

Thanks. Looks good to me. @asundqui good to go?

[asundqui]

Probably good to go, but can I test on Quest 3 and AVP tonight to make sure?

[mrxz]

Probably good to go, but can I test on Quest 3 and AVP tonight to make sure?

FYI, I've tested it on a Quest 3 myself, but more testing never hurts. :-)

[asundqui]

Looks like your code cleans things up and makes it simpler :). I checked on AVP additionally and everything checks out. Let's merge this yes @dmarcos thanks guys!

[dmarcos]

Thanks