* Update to wgpu 0.9
* Fix validation error in WGSL shader
- This moves the hardcoded vertex positions and texture coordinates to
the vertex buffer.
- Replaces the two-triangle quad to 1 full-screen triangle (fixes#180)
- Rewrites the custom shader example to fix a bug with large surface
textures;
- The input texture size was used for the output texture, causing the
purple rectangle to appear very jumpy on large displays in full screen.
- The `ScalingRenderer` now exposes its clipping rectangle. The custom
shader example uses this for its own clipping rectangle, but it can
also be used for interacting with the border in general.
* Switch to `wgpu::include_wgsl!()`
- This is a nice little simplification.
- Thanks to @JMS55 for the suggestion!
