You can now build with STYLE_INVALIDATION_DEBUG and get a debug stream
of reasons why style invalidations are happening and where.
I've rewritten this code many times, so instead of throwing it away once
again, I figured we should at least have it behind a flag.
(cherry picked from commit ddbfac38b0074819470766846fca08fd78630eb0;
minorly amended for conflicts in AK/Debug.h.in and
Meta/CMake/all_the_debug_macros.cmake due to us having more debug
macros. Also, downstream got alphabetical order for
STYLE_INVALIDATION_DEBUG wrong.)
