Draft: d3d11: wined3d: Implement texture reduction mode
This is a hacky, unfinished implementation of the "texture reduction mode" features found in d3d11, on top of ARB_texture_filter_minmax.
It turns out the game I was debugging doesn't even use this, so I haven't tested it yet, and possibly won't get back to it soon, but maybe it'll be useful to someone.
Still needed:
- d3d11 shouldn't report this if ARB_texture_filter_minmax isn't present.
- Probably support EXT_texture_filter_minmax as well.
- Add support to the Vulkan backend (see VkSamplerReductionModeCreateInfo)
- Remove some debug WARN()s and other cleanups.