[clang] [clang][analyzer] Move 'alpha.core.PointerSub' checker into 'core.PointerSub' (PR #107596)

[Balázs Kéri via cfe-commits]

balazske wrote:

I moved the checker now into package `security`. The main reason is that the checker should not be turned on by default because  use of such low-level features may be valid in some projects. The checker is not absolutely security-related but there was no better place for it (`optin` is for checkers that are turned off more often). I need a re-approval before merge.

https://github.com/llvm/llvm-project/pull/107596