[wgpu] Expose wgpu::Adapter via RenderState (#2954)

* [wgpu] Expose adapter, better errors, better docs, more code sharing, use stencil bits

* doc fix

* remove unnecessary unsafe

* handle missing framebuffer format

* better handling of renderstate creation in winit.rs

* remove unnecessary use directive

Cargo.lock

@@ -1251,6 +1251,7 @@ dependencies = [
  "epaint",
  "log",
  "puffin",
+ "thiserror",
  "type-map",
  "wgpu",
  "winit",