350: Implement Extensions Interface r=kvark a=cwfitzgerald
This implements https://github.com/gfx-rs/wgpu/pull/703 in wgpu-rs. Notable changes include the removal of the anisotropic field from the examples, in favor of the now mandatory `..Default::default()` syntax.
Co-authored-by: Connor Fitzgerald <connorwadefitzgerald@gmail.com>