[clang] [Clang] Implement the 'counted_by' attribute (PR #76348)

[via cfe-commits]

dyung wrote:

@bwendling the test you added `CodeGen/attr-counted-by.c` appears to be failing on quite a few bots, can you take a look?

Some failing bots:
- https://lab.llvm.org/buildbot/#/builders/164/builds/48660
- https://lab.llvm.org/buildbot/#/builders/188/builds/40261
- https://lab.llvm.org/buildbot/#/builders/245/builds/18987
- https://lab.llvm.org/buildbot/#/builders/258/builds/12107
- https://lab.llvm.org/buildbot/#/builders/249/builds/13974
- https://lab.llvm.org/buildbot/#/builders/230/builds/23480
- https://lab.llvm.org/buildbot/#/builders/124/builds/9378
- https://lab.llvm.org/buildbot/#/builders/67/builds/14012
- https://lab.llvm.org/buildbot/#/builders/98/builds/31297
- https://lab.llvm.org/buildbot/#/builders/247/builds/13055
- https://lab.llvm.org/buildbot/#/builders/139/builds/56868
- https://lab.llvm.org/buildbot/#/builders/216/builds/32771
- https://lab.llvm.org/buildbot/#/builders/275/builds/3146
- https://lab.llvm.org/buildbot/#/builders/272/builds/5208
- https://lab.llvm.org/buildbot/#/builders/271/builds/2686

https://github.com/llvm/llvm-project/pull/76348