Expand the imported texture channel count for remapping if necessary

[BlueCube3310]

Fixes #106422

Manages the remapped channel count in a sophisticated way that expands their amount only when said channel is necessary. This ensures that the memory usage, as well as extended import times due to format conversion, are kept to the minimum.

This needs a lot of testing. From my own, it looks like it works as intended, though since it's a complicated change it would be best to ensure it works for as many remap/format combinations as possible.

[Calinou]

Tested locally with the MRP from #106422, it works as expected. Code looks good to me.

master	This PR

[LiveTrower]

I've tried various textures and combinations, and I found a detail that I don't quite understand.

I'm going to give two examples:

First, an RGB texture where we set the Green and Blue channels to Zero, leaving only the Red channel, gives us this result.

But if we change the Red channel to Zero and the Green channel to its default value, the Alpha channel appears, which didn't happen in the previous example.

Is this a bug?

[BlueCube3310]

Is this a bug?

It is, I noticed it too but it looks like it's related to the Image function that detects the used channels. I'll look into it as well

[fire]

It is, I noticed it too but it looks like it's related to the Image function that detects the used channels. I'll look into it as well

does this need to be resolved before merge?

[BlueCube3310]

It is, I noticed it too but it looks like it's related to the Image function that detects the used channels. I'll look into it as well

does this need to be resolved before merge?

I figured out what causes this, it's a fairly simple fix but I would like to make a separate PR for that.

[Repiteo]

Thanks!