Add OutputCommand::SetPointerPosition to set mouse position (#5776)

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This is not supported on the web and not yet on Wayland.

~~I also had to update `ring` and add an exception for `paste` being
unmaintained.~~ Has since been updated on master.

* [x] I have followed the instructions in the PR template

crates/eframe/src/web/app_runner.rs

@@ -336,6 +336,9 @@ impl AppRunner {
                 egui::OutputCommand::OpenUrl(open_url) => {
                     super::open_url(&open_url.url, open_url.new_tab);
                 }
+                egui::OutputCommand::SetPointerPosition(_) => {
+                    // Not supported on the web.
+                }
             }
         }