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.

scene/resources/segment_shape_2d.cpp

@@ -51,6 +51,7 @@ void SegmentShape2D::set_a(const Vector2 &p_a) {
 	a = p_a;
 	_update_shape();
 }
+
 Vector2 SegmentShape2D::get_a() const {
 	return a;
 }
@@ -59,6 +60,7 @@ void SegmentShape2D::set_b(const Vector2 &p_b) {
 	b = p_b;
 	_update_shape();
 }
+
 Vector2 SegmentShape2D::get_b() const {
 	return b;
 }
@@ -148,6 +150,7 @@ void RayShape2D::set_length(real_t p_length) {
 	length = p_length;
 	_update_shape();
 }
+
 real_t RayShape2D::get_length() const {
 	return length;
 }