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/math/vector3i.cpp

@@ -34,6 +34,7 @@ void Vector3i::set_axis(int p_axis, int32_t p_value) {
 	ERR_FAIL_INDEX(p_axis, 3);
 	coord[p_axis] = p_value;
 }
+
 int32_t Vector3i::get_axis(int p_axis) const {
 	ERR_FAIL_INDEX_V(p_axis, 3, 0);
 	return operator[](p_axis);
@@ -42,6 +43,7 @@ int32_t Vector3i::get_axis(int p_axis) const {
 int Vector3i::min_axis() const {
 	return x < y ? (x < z ? 0 : 2) : (y < z ? 1 : 2);
 }
+
 int Vector3i::max_axis() const {
 	return x < y ? (y < z ? 2 : 1) : (x < z ? 2 : 0);
 }