Optimize TextureBuilder creations with no initial data
* Use vkCmdClearColorImage instead of allocating a big empty buffer in
managed
* Texture.CreateInternal also passes a nullptr if the span is empty, so we
don't do additional unnecessary setdata
It's weird all of this stuff has an API of Span<T> & int length, but hard
to fix without API breaking changes
DrawIndirectArguments should be LayoutKind.Sequential