Rename "convert.h" to "event_converter.h"

The filename gave no hint about what was converted.

app/meson.build

@@ -3,10 +3,10 @@ src = [
     'src/command.c',
     'src/control_msg.c',
     'src/controller.c',
-    'src/convert.c',
     'src/decoder.c',
     'src/device.c',
     'src/device_msg.c',
+    'src/event_converter.c',
     'src/file_handler.c',
     'src/fps_counter.c',
     'src/input_manager.c',

app/src/event_converter.c

@@ -1,4 +1,4 @@
-#include "convert.h"
+#include "event_converter.h"
 
 #define MAP(FROM, TO) case FROM: *to = TO; return true
 #define FAIL default: return false

app/src/input_manager.c

@@ -1,7 +1,7 @@
 #include "input_manager.h"
 
 #include <SDL2/SDL_assert.h>
-#include "convert.h"
+#include "event_converter.h"
 #include "lock_util.h"
 #include "log.h"