[clang] [clang][diagnostics] Add `-fdiagnostics-add-output` switch for SARIF (PR #185201)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

Thank you for working on this and my deep apologies for the delay in review. Overall, I like the direction this is heading. I did have a question about what interface should be responsible for handling file system mechanics and when we want the point of failure if an output file cannot be opened.

Please be sure to add a release note to `clang/docs/ReleaseNotes.rst`.

https://github.com/llvm/llvm-project/pull/185201