Loaders: Stop usage of RGBFormat.

[Mugen87]

Related issue: -

Description

We can't use RGBELoader with WebGPURenderer right now since the loader returns RGB textures. 3 channel formats are not supported with WebGPU. And also in context of WebGL it's recommended to always use RBGA since RGB might be emulated (e.g. with a Metal backend).

[Mugen87]

@gkjohnson I did not touch LUT3dlLoader since there is no example for testing and I did not fully understand the index and scale logic in parse(). Can you take care of it?

[gkjohnson]

I've create #23202 which adds a 3DL example file. I'll take a look at removing the RGBFormat use over the next few days.

[mrdoob]

Thanks!