[clang] [analyzer] Introduce the check::BlockEntrance checker callback (PR #140924)

[Balázs Benics via cfe-commits]

balazs-benics-sonarsource wrote:

> @steakhal Thanks for the updates, I'm completely satisfied with them.
> 
> I don't see any connection between this commit and the buildbot failures 🤔 ... they are probably unrelated.

About 90% of the time they are unrelated. I don't usually put a confirmation to these messages.

https://github.com/llvm/llvm-project/pull/140924