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.

drivers/unix/os_unix.cpp

@@ -244,6 +244,7 @@ void OS_Unix::delay_usec(uint32_t p_usec) const {
 	while (nanosleep(&rem, &rem) == EINTR) {
 	}
 }
+
 uint64_t OS_Unix::get_ticks_usec() const {
 #if defined(__APPLE__)
 	uint64_t longtime = mach_absolute_time() * _clock_scale;