Update to wgpu 0.14 (#2114)

crates/eframe/src/web/web_painter_wgpu.rs

@@ -115,6 +115,7 @@ impl WebPainter for WebPainterWgpu {
                     width: canvas_size[0],
                     height: canvas_size[1],
                     present_mode: wgpu::PresentMode::Fifo,
+                    alpha_mode: wgpu::CompositeAlphaMode::Auto,
                 },
             );
             self.surface_size = canvas_size.clone();