[wpigui] Add OpenURL (#4273)

This function opens a URL using the default browser.

wpigui/src/main/native/include/wpigui_openurl.h

@@ -0,0 +1,18 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#pragma once
+
+#include <string>
+
+namespace wpi::gui {
+
+/**
+ * Opens a URL in the default browser.
+ *
+ * @param url URL to open
+ */
+void OpenURL(const std::string& url);
+
+}  // namespace wpi::gui