xwayland/glx: Enable sRGB fbconfigs
We turn this on if the GL underneath us can enable GL_FRAMEBUFFER_SRGB. However we don't generate both capable and incapable configs, which is unlike the DRI backend, but matches NVIDIA.
We turn this on if the GL underneath us can enable GL_FRAMEBUFFER_SRGB. However we don't generate both capable and incapable configs, which is unlike the DRI backend, but matches NVIDIA.