[analyzer][clang-tidy] Consume reports and FixIts from --export-fixes YAML output instead of stdout/stderr

[whisperity]

Extracted from #4052

We should consider dropping the conversion from "random meaningless stdout text"-to-plist in favour of "well-formatted message and fix YAML"-to-plist. (Or SARIF?)

For a very long time now, Clang-Tidy was capable of dumping the structure of the created diagnostics (all the notes, warnings, and fixits, see https://github.com/llvm/llvm-project/blob/llvmorg-17.0.0/clang-tools-extra/test/clang-tidy/infrastructure/export-diagnostics.cpp!) in YAML.

[whisperity]

Something changed likely after LLVM 18.0 was snapshotted and work on 19.0 begun, because now I'm seeing the following bogus parses from CodeChecker. | and ~~~~~~~~~ alone on lines are definitely not the right fixits.