[clang] [NFC][analyzer] Document configuration options (PR #135169)

[Donát Nagy via cfe-commits]

NagyDonat wrote:

@steakhal I implemented most of your review suggestions (the only missing thing is that I'll set up a test to validate that this script can parse `AnalyzerOptions.def`).

Please check the wording of the disclaimers added by https://github.com/llvm/llvm-project/pull/135169/commits/461d3db784bd66574c9d175dbc8f5e7190342b8e because I'm not too confident about them. (In particular, you suggested that I should add a disclaimer about the malleable state of `clang -cc1` flags, but there is no more stable alternative for specifying analyzer flags _and_ `-analyzer-config` is unchanged since 2017, so I also added an "anti-disclaimer" sentence. There is probably a better solution than this...)

https://github.com/llvm/llvm-project/pull/135169