Fix text input event segfault

The text input control_event was initially designed for mapping
SDL_TextInputEvent, limited to 32 characters.

For simplicity, the copy/paste feature was implemented using the same
control_event: it just sends the text to paste.

However, the pasted text might have a length breaking some assumptions:
 - on the client, the event max-size was smaller than the text
   max-length,
 - on the server, the raw buffer storing the events was smaller than the
   max event size.

Fix these inconsistencies, and encode the length on 2 bytes, to accept
more than 256 characters.

Fixes <https://github.com/Genymobile/scrcpy/issues/10>.

app/src/controlevent.h

@@ -9,8 +9,8 @@
 #include "common.h"
 
 #define CONTROL_EVENT_QUEUE_SIZE 64
-#define SERIALIZED_EVENT_MAX_SIZE 33
-#define TEXT_MAX_LENGTH 256
+#define TEXT_MAX_LENGTH 300
+#define SERIALIZED_EVENT_MAX_SIZE 3 + TEXT_MAX_LENGTH
 
 enum control_event_type {
     CONTROL_EVENT_TYPE_KEYCODE,