Update to wgpu 0.20 (#4560)

* this PR reverts https://github.com/emilk/egui/pull/4559
* and re-applies https://github.com/emilk/egui/pull/4433

Before we merge, we're waiting for a wgpu 0.20.1 patch-release of

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

---------

Co-authored-by: Andreas Reich <r_andreas2@web.de>

crates/egui-wgpu/src/renderer.rs

@@ -294,6 +294,7 @@ 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,
@@ -335,6 +336,7 @@ impl Renderer {
                         }),
                         write_mask: wgpu::ColorWrites::ALL,
                     })],
+                    compilation_options: wgpu::PipelineCompilationOptions::default()
                 }),
                 multiview: None,
             }