This PR contains only the docs changes of #102435, in case the production team believes these docs changes would be good to incorporate into the 4.4 release separate from the other PR, which won't be in its final highly optimized state until a few weeks from now. These docs changes do not depend on the changes from the other PR.

These docs changes better describe the new AgX tonemapper that is introduced with 4.4.

They also make the tonemapper descriptions consistent with each other, making them easier to quickly compare. They follow this format:

1. Description of tonemapping curve.
2. Key properties and their impact on the resulting image.
3. Performance characteristic relative to other tonemappers.
4. Additional notes, if required.

I have also updated the white and exposure documentation along with this refresh.

Once this PR is approved and editing is finished, I will open a sibling PR to update the online docs.