Add GET_CLIPBOARD device event

Add the first device event, used to forward the device clipboard to the
computer.

app/tests/test_device_event_deserialize.c

@@ -0,0 +1,28 @@
+#include <assert.h>
+#include <string.h>
+
+#include "device_event.h"
+
+#include <stdio.h>
+static void test_deserialize_clipboard_event(void) {
+    const unsigned char input[] = {
+        0x00, // DEVICE_EVENT_TYPE_CLIPBOARD
+        0x00, 0x03, // text length
+        0x41, 0x42, 0x43, // "ABC"
+    };
+
+    struct device_event event;
+    ssize_t r = device_event_deserialize(input, sizeof(input), &event);
+    assert(r == 6);
+
+    assert(event.type == DEVICE_EVENT_TYPE_GET_CLIPBOARD);
+    assert(event.clipboard_event.text);
+    assert(!strcmp("ABC", event.clipboard_event.text));
+
+    device_event_destroy(&event);
+}
+
+int main(void) {
+    test_deserialize_clipboard_event();
+    return 0;
+}