Rename "event" to "message"

After the recent refactorings, a "control event" is not necessarily an
"event" (it may be a "command"). Similarly, the unique "device event"
used to send the device clipboard content is more a "reponse" to the
request from the client than an "event".

Rename both to "message", and rename the message types to better
describe their intent.

app/src/control_msg.h

@@ -0,0 +1,64 @@
+#ifndef CONTROLMSG_H
+#define CONTROLMSG_H
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+
+#include "android/input.h"
+#include "android/keycodes.h"
+#include "common.h"
+
+#define CONTROL_MSG_TEXT_MAX_LENGTH 300
+#define CONTROL_MSG_CLIPBOARD_TEXT_MAX_LENGTH 4093
+#define CONTROL_MSG_SERIALIZED_MAX_SIZE \
+    (3 + CONTROL_MSG_CLIPBOARD_TEXT_MAX_LENGTH)
+
+enum control_msg_type {
+    CONTROL_MSG_TYPE_INJECT_KEYCODE,
+    CONTROL_MSG_TYPE_INJECT_TEXT,
+    CONTROL_MSG_TYPE_INJECT_MOUSE_EVENT,
+    CONTROL_MSG_TYPE_INJECT_SCROLL_EVENT,
+    CONTROL_MSG_TYPE_BACK_OR_SCREEN_ON,
+    CONTROL_MSG_TYPE_EXPAND_NOTIFICATION_PANEL,
+    CONTROL_MSG_TYPE_COLLAPSE_NOTIFICATION_PANEL,
+    CONTROL_MSG_TYPE_GET_CLIPBOARD,
+    CONTROL_MSG_TYPE_SET_CLIPBOARD,
+};
+
+struct control_msg {
+    enum control_msg_type type;
+    union {
+        struct {
+            enum android_keyevent_action action;
+            enum android_keycode keycode;
+            enum android_metastate metastate;
+        } inject_keycode;
+        struct {
+            char *text; // owned, to be freed by SDL_free()
+        } inject_text;
+        struct {
+            enum android_motionevent_action action;
+            enum android_motionevent_buttons buttons;
+            struct position position;
+        } inject_mouse_event;
+        struct {
+            struct position position;
+            int32_t hscroll;
+            int32_t vscroll;
+        } inject_scroll_event;
+        struct {
+            char *text; // owned, to be freed by SDL_free()
+        } set_clipboard;
+    };
+};
+
+// buf size must be at least CONTROL_MSG_SERIALIZED_MAX_SIZE
+// return the number of bytes written
+size_t
+control_msg_serialize(const struct control_msg *msg, unsigned char *buf);
+
+void
+control_msg_destroy(struct control_msg *msg);
+
+#endif