Press COPY on "get clipboard" request if possible

If the device runs at least Android 7, just press COPY on the device
(the clipboard content will be sent via the clipboard listener).

<https://developer.android.com/reference/android/view/KeyEvent.html#KEYCODE_COPY>

app/tests/test_control_msg_serialize.c

@@ -185,14 +185,18 @@ static void test_serialize_collapse_notification_panel(void) {
 static void test_serialize_get_clipboard(void) {
     struct control_msg msg = {
         .type = CONTROL_MSG_TYPE_GET_CLIPBOARD,
+        .get_clipboard = {
+            .copy = true,
+        },
     };
 
     unsigned char buf[CONTROL_MSG_SERIALIZED_MAX_SIZE];
     int size = control_msg_serialize(&msg, buf);
-    assert(size == 1);
+    assert(size == 2);
 
     const unsigned char expected[] = {
         CONTROL_MSG_TYPE_GET_CLIPBOARD,
+        1, // copy
     };
     assert(!memcmp(buf, expected, sizeof(expected)));
 }