implement clipboard on iOS

src/app_events.cpp

@@ -8,8 +8,30 @@ void android_pick_file(android_app* mApplication, std::function<void(std::string
 std::string win32_open_file(const char* filter);
 std::string win32_open_dir();
 void win32_show_cursor(bool visible);
+bool win32_clipboard_set_text(const std::string & s);
+std::string win32_clipboard_get_text();
 #endif
 
+
+std::string App::clipboard_get_text()
+{
+#if _WIN32
+    return win32_clipboard_get_text();
+#elif __IOS__
+    return [ios_view clipboard_get_string];
+#endif
+}
+
+bool App::clipboard_set_text(const std::string& s)
+{
+#if _WIN32
+    return win32_clipboard_set_text(s);
+#elif __IOS__
+    return [ios_view clipboard_set_string:s];
+#endif
+}
+
+
 void App::crash_test()
 {
 #ifdef __IOS__