Paste on "set clipboard" if possible

Ctrl+Shift+v synchronizes the computer clipboard to the Android device
clipboard. This feature had been added to provide a way to copy UTF-8
text from the computer to the device.

To make such a paste more straightforward, if the device runs at least
Android 7, also send a PASTE keycode to paste immediately.

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

Fixes #786 <https://github.com/Genymobile/scrcpy/issues/786>

app/tests/test_control_msg_serialize.c

@@ -201,16 +201,18 @@ static void test_serialize_set_clipboard(void) {
     struct control_msg msg = {
         .type = CONTROL_MSG_TYPE_SET_CLIPBOARD,
         .set_clipboard = {
+            .paste = true,
             .text = "hello, world!",
         },
     };
 
     unsigned char buf[CONTROL_MSG_SERIALIZED_MAX_SIZE];
     int size = control_msg_serialize(&msg, buf);
-    assert(size == 16);
+    assert(size == 17);
 
     const unsigned char expected[] = {
         CONTROL_MSG_TYPE_SET_CLIPBOARD,
+        1, // paste
         0x00, 0x0d, // text length
         'h', 'e', 'l', 'l', 'o', ',', ' ', 'w', 'o', 'r', 'l', 'd', '!', // text
     };