Style: Enforce separation line between function definitions

I couldn't find a tool that enforces it, so I went the manual route:
```
find -name "thirdparty" -prune \
  -o -name "*.cpp" -o -name "*.h" -o -name "*.m" -o -name "*.mm" \
  -o -name "*.glsl" > files
perl -0777 -pi -e 's/\n}\n([^#])/\n}\n\n\1/g' $(cat files)
misc/scripts/fix_style.sh -c
```

This adds a newline after all `}` on the first column, unless they
are followed by `#` (typically `#endif`). This leads to having lots
of places with two lines between function/class definitions, but
clang-format then fixes it as we enforce max one line of separation.

This doesn't fix potential occurrences of function definitions which
are indented (e.g. for a helper class defined in a .cpp), but it's
better than nothing. Also can't be made to run easily on CI/hooks so
we'll have to be careful with new code.

Part of #33027.

core/input/input.cpp

@@ -672,6 +672,7 @@ void Input::set_mouse_position(const Point2 &p_posf) {
 Point2 Input::get_mouse_position() const {
 	return mouse_pos;
 }
+
 Point2 Input::get_last_mouse_speed() const {
 	return mouse_speed_track.speed;
 }
@@ -812,6 +813,7 @@ void Input::accumulate_input_event(const Ref<InputEvent> &p_event) {
 
 	accumulated_events.push_back(p_event);
 }
+
 void Input::flush_accumulated_events() {
 	while (accumulated_events.front()) {
 		parse_input_event(accumulated_events.front()->get());