WebGPURenderer: Resize breaks post FX setup in webgpu_rtt example

[RenaudRohlinger]

Description

When using a quadMesh to perform a post FX render any resize of the window will break the renderer and render a black screen.
I suspect the texture of the new FBO to not be properly bind back once the previous one was destroyed.

Reproduction steps

1. Run the webgpu_rtt.html example under the WebGL Backend.
2. Resize the window

Live example

• https://threejs.org/examples/?q=gpu%20mu#webgpu_rtt (WebGL Backend)

Version

r160

[RenaudRohlinger]

I fixed it on my local. Will push a bit later as I added MSAA support to the WebGLBackend and fixed that issue in the process and I would like to make a better demo.
It was related to the fact the framebuffers were never cleared. 👍