Implement the GT7 tonemapper for HDR Display Output

## What problem does this solve or what need does it fill?

None of our current tonemappers work for HDR display output. It hasn't mattered until now because we haven't supported HDR display output until https://github.com/bevyengine/bevy/pull/22563 (HDR Display Output here isn't referring to the current Hdr setting on `Camera`s which only changes the intermediate texture formats, but instead refers to displaying an HDR surface to the user).

## What solution would you like?

Implement the GT7 tonemapper. It supports both HDR and SDR output, and looks good.
https://s3.amazonaws.com/gran-turismo.com/pdi_publications/s2025_PBS_Physically_Based_Tone_Mapping_GT7.pdf

Start by reading the linked GT7 Physically Based Tone Mapping paper and reviewing Bevy's existing tonemappers alongside the HDR display-output work referenced in PR #22563. Determine the appropriate rendering entry point and how the new operator must handle both HDR and SDR output; done means the GT7 tonemapper is implemented and produces suitable output in both modes.

Written by the indexing model from the issue text.