This adds the `Half Float Precision` option in the image property panel.
This option is only available on float textures and is enabled by default.
Adding a flag inside the imbuf (IB_halffloat) on load is done for EXR and PSD formats that can store half floating point (16bits/channels).
The option is then not displayed in this case and forced.
Related task T73086
Reviewed By: brecht
Differential Revision: https://developer.blender.org/D6891
4e9fffc289