[clang] [analyzer] Delay the checker constructions after parsing (PR #127409)

[Gábor Horváth via cfe-commits]

Xazax-hun wrote:

> FYI: This may be a breaking change to some downstream users that may had some means to attach different listeners and what not to e.g. the Preprocessor inside their checker register functions. Since we delay the calls to these register fns after parsing is already done, they would of course miss the parsing Preprocessor events.

I am OK with this tradeoff but wondering if it is possible to add back support. E.g., having a special pre-parsing callback that can do this sort of setup (but does not do any registration yet). 

https://github.com/llvm/llvm-project/pull/127409