QSurfaceFormat usage of QColorSpace not useful for 3D APIs and real-world HDR formats

Hi,

In Qt6 the QSurfaceFormat::ColorSpace enum was deprecated in favour of using ICC profile-backed QColorSpace instances. I believe this prevents users of OpenGL bindings from requesting HDR surfaces, because this enforces the transfer curve to be one of the supported ICC types (specifically type 4 as per QColorTransferFunction). This restriction leaves the only alternative of Rhi as the graphics backend (and by extension requiring a migration to Qt Quick, to the best of my knowledge).

With this report, I'm targeting specifically support for PQ/HLG which are the only ones available eg. with DirectX for BT.2020 content.

For further context, I think https://bugs.chromium.org/p/chromium/issues/detail?id=1038494 is also useful.