Revert update to wgpu 0.20 => downgrade to wgpu 0.19.1 (#4559)

0.20 has a bunch of bugs that will be fixed by:

* https://github.com/gfx-rs/wgpu/pull/5681

At Rerun, we don't want to wait for the wgpu 0.20.1 patch release before
we update egui, so we will temporarily downgrade to wgpu 0.19

After reverting I'll open a new PR that will update to 0.20 again, with
the intention of merging that once 0.20.1 is released.

crates/egui-wgpu/src/renderer.rs

@@ -294,7 +294,6 @@ impl Renderer {
                         // 2: uint color
                         attributes: &wgpu::vertex_attr_array![0 => Float32x2, 1 => Float32x2, 2 => Uint32],
                     }],
-                    compilation_options: wgpu::PipelineCompilationOptions::default()
                 },
                 primitive: wgpu::PrimitiveState {
                     topology: wgpu::PrimitiveTopology::TriangleList,
@@ -336,7 +335,6 @@ impl Renderer {
                         }),
                         write_mask: wgpu::ColorWrites::ALL,
                     })],
-                    compilation_options: wgpu::PipelineCompilationOptions::default()
                 }),
                 multiview: None,
             }