[vk] Request VK_KHR_sampler_mirror_clamp_to_edge when Features::SAMPLER_MIRROR_CLAMP_EDGE is set

Currently the feature is checked here:

Lines 1151 to 1153 in a76e687

    
           if self.supports_extension(vk::KhrSamplerMirrorClampToEdgeFn::name()) { 
        
               bits |= Features::SAMPLER_MIRROR_CLAMP_EDGE; 
        
           }

But not added to the enabled extensions list when actually opening the device here:

gfx/src/backend/vulkan/src/lib.rs

Line 780 in a76e687

let enabled_extensions = {

In Vulkan 1.2 this feature has been promoted and is guaranteed to be supported. Currently gfx doesn't request the extension in < 1.2 and gfx may incorrectly say it does not have support for Features::SAMPLER_MIRROR_CLAMP_EDGE since in 1.2 support for the extension itself is optional.

	if self.supports_extension(vk::KhrSamplerMirrorClampToEdgeFn::name()) {
	bits \|= Features::SAMPLER_MIRROR_CLAMP_EDGE;
	}