Minimize include dependencies of display_server.h

- Removes `native_menu.h` dependency from `display_server.h`.
  It's now forward-declared in all DisplayServer implementations and should
  be included in the .cpp's.
- Removes some unused `rb_set.h` and `rb_map.h` dependencies, which leads to
  having to include them explicitly in half the scene and editor codebase...
  which shows how much we depend on `display_server.h`.
- Forward-declare `input_event.h`, so now we need only `keyboard.h`.

platform/android/display_server_android.cpp

@@ -37,6 +37,8 @@
 
 #include "core/config/project_settings.h"
 #include "core/input/input.h"
+#include "core/input/input_event.h"
+#include "servers/display/native_menu.h"
 
 #if defined(RD_ENABLED)
 #include "servers/rendering/renderer_rd/renderer_compositor_rd.h"