Don't scroll when pressing space on a focused canvas

After reaching keypress, we should prevent further propagation.

Relates to #1741

src/platform_impl/web/stdweb/canvas.rs

@@ -165,6 +165,8 @@ impl Canvas {
         // viable/compatible alternative as of now. `beforeinput` is still widely
         // unsupported.
         self.on_received_character = Some(self.add_user_event(move |event: KeyPressEvent| {
+            // Supress further handling to stop keys like the space key from scrolling the page.
+            event.prevent_default();
             handler(event::codepoint(&event));
         }));
     }

src/platform_impl/web/web_sys/canvas.rs

@@ -189,6 +189,8 @@ impl Canvas {
         self.on_received_character = Some(self.common.add_user_event(
             "keypress",
             move |event: KeyboardEvent| {
+                // Supress further handling to stop keys like the space key from scrolling the page.
+                event.prevent_default();
                 handler(event::codepoint(&event));
             },
         ));