* enable CLEAR_COMMANDS feature for all adapters
* replaced fill_buffer with clear_buffer (minus variable value)
* Improve clear buffer/texture test
and remove unused clear-buffer.ron test
* renamed clear_image to clear_texture
* skeleton for new wgpu-hal clear_texture
* clear_texture implementation for vulkan
* clear_texture now restricts usage
* clear_texture implementation for dx12
* Implemented clear_texture for Metal backend
* Clean up GLES clear_buffer and leave note on how to implement clear_texture in the future
* fix linux compilation & formatting issues
* comment & namespace fixes
* Extent3d has now a simple mipmap calculating function
Fix incorrect use of texture.size in clear_texture for metal/dx12
Fix incorrect mip/layer ranges in clear_texture for metal/dx12