Add a 4th check that compares IDL-generated file sets between
configure.py and CMake. Previously only compilation flags, link
targets, and linker settings were compared — a missing IDL entry
(like strong_consistency/groups_manager.idl.hh in PR #28843) would
go undetected.
The extractors parse ninja build statements from both systems and
normalize to a canonical relative path (e.g. cache_temperature.dist.hh)
for comparison. configure.py outputs are filtered by mode; CMake
outputs handle the | separator for implicit outputs in ninja build
lines.
Also update the documentation to mention the new check.
Document the purpose, usage, and examples for
scripts/compare_build_systems.py which compares the configure.py
and CMake build systems by parsing their ninja build files.
