[clang] [clang][analyzer] Move 'alpha.core.FixedAddressDereference' out of alpha (PR #132404)

[Balázs Benics via cfe-commits]

steakhal wrote:

I am getting some push back internally against this change.

The problem is that some projects are close-to-the-metal (firmware, boot, hardware stuff) and there actually the only way to communicate with the hardware is via fixed addresses and a bunch of volatile pointers.

Of course, this checker wasn't really designed for such code bases - if anything, for the opposite.
However, projects in such a domain are also likely to have a security aware mindset, which fundamentally opposes them to just disable some checkers - especially if they are in the `core` package. I find this argument pretty solid.

So the question is, why should we do about this?
 - Clarify the docs that this checker is not intended to be used in firmware stuff?
 - I want to especially avoid the users picking up the only suppression to this checker, using the `address_space(NNN)` attribute. That attribute is not documented, also has consequences on the binary so I definitely don't want to imply using that for suppression. This is kinda what users think right now, sadly.
 - Come up with some new way of suppressing this checker?
 - We could potentially move this to the `optin` package.
 
 @NagyDonat @balazske WDYT?

https://github.com/llvm/llvm-project/pull/132404