[llvm-branch-commits] [clang-doc][NFC] Make test resilient to line changes (PR #119811)

[Paul Kirth via llvm-branch-commits]

https://github.com/ilovepi created https://github.com/llvm/llvm-project/pull/119811

This just reorganizes the test code, so its easy to use @LINE directives
in the test, and avoid needing to update all the line numbers when making
unrelated changes.