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.

modules/gridmap/grid_map.cpp

@@ -197,6 +197,7 @@ void GridMap::set_cell_size(const Vector3 &p_size) {
 	_recreate_octant_data();
 	emit_signal("cell_size_changed", cell_size);
 }
+
 Vector3 GridMap::get_cell_size() const {
 	return cell_size;
 }
@@ -206,6 +207,7 @@ void GridMap::set_octant_size(int p_size) {
 	octant_size = p_size;
 	_recreate_octant_data();
 }
+
 int GridMap::get_octant_size() const {
 	return octant_size;
 }