Forward Ctrl to the device

Now that the scrcpy shortcut modifier is Alt by default (and can be
configured), forward Ctrl to the device.

This allows to trigger Android shortcuts.

Fixes #555 <https://github.com/Genymobile/scrcpy/issues/555>

app/src/event_converter.c

@@ -92,6 +92,8 @@ convert_keycode(SDL_Keycode from, enum android_keycode *to, uint16_t mod,
         MAP(SDLK_LEFT,         AKEYCODE_DPAD_LEFT);
         MAP(SDLK_DOWN,         AKEYCODE_DPAD_DOWN);
         MAP(SDLK_UP,           AKEYCODE_DPAD_UP);
+        MAP(SDLK_LCTRL,        AKEYCODE_CTRL_LEFT);
+        MAP(SDLK_RCTRL,        AKEYCODE_CTRL_RIGHT);
     }
 
     if (!(mod & (KMOD_NUM | KMOD_SHIFT))) {
@@ -111,8 +113,8 @@ convert_keycode(SDL_Keycode from, enum android_keycode *to, uint16_t mod,
         }
     }
 
-    if (prefer_text) {
+    if (prefer_text && !(mod & KMOD_CTRL)) {
-        // do not forward alpha and space key events
+        // do not forward alpha and space key events (unless Ctrl is pressed)
         return false;
     }