[clang] [analyzer] Model Microsoft "__assume" in the same way as clang "__builtin_assume" (PR #80456)

[Balazs Benics via cfe-commits]

steakhal wrote:

Thanks Donát!

I'll wait for @Xazax-hun explicit approval to be sure everyone on board (who left remarks) are okay with the current content.

https://github.com/llvm/llvm-project/pull/80456