cmSarif: Improve conformance with SARIF in CMake result reporting

Reorganize CMake's SARIF implementation to clearly distinguish between the SARIF standard and CMake's result reporting structure, fixing several validation failures.
- Removed unused message strings in reported rules.
- Report artifact locations relative to the CMake home directory.
- Use the recommended schema URL.
- Stop reporting some invalid locations read from the top of the stack.

cmMessenger no longer manages a SARIF log but stores a list of displayed messages. The SARIF log is constructed from displayed messages upon writing the file.