Compatible with Clang 18.
Major changes:
- [iwyu] Improve type analysis for typedefs, aliases and templates
- [iwyu] Improve analysis of macros expanding macros
- [iwyu] Improve IWYU driver for better validation and job handling
- [iwyu] Reject IWYU invocations with precompiled headers (see FAQ)
- [iwyu_tool] Better preserve failure exit codes
- [mappings] Add mappings for libstdc++
<debug/...>headers - [mappings] Make mappings for POSIX and standard C headers stricter (more portable)
- [doc] Add separate FAQ page for longer descriptions
- [ci] IWYU now runs on itself in CI (finally!)
... and many smaller improvements