[clang][NFC] Move Bounds Safety Sema code to `SemaBoundsSafety.cpp` (#99330)

This patch adds a new `SemaBoundsSafety.cpp` source file and moves the
existing `CheckCountedByAttrOnField` function and related helper
functions and types from `SemaDeclAttr.cpp` into the new source file.
The `CheckCountedByAttrOnField` function is now a method on the Sema
class and now has doxygen comments.

The goal behind this refactor is to clearly separate the
`-fbounds-safety` Sema code from everything else.

Although `counted_by(_or_null)` and `sized_by(_or_null)` attributes have
a meaning outside of `-fbounds-safety` it seems reasonable to also have
the Sema logic live in `SemaBoundsSafety.cpp` since the intention is
that the attributes will have the same semantics (but not necessarily
the same enforcement).

As `-fbounds-safety` is upstreamed additional Sema checks will be added
to `SemaBoundsSafety.cpp`.

rdar://131777237

0 files changed, 0 insertions, 0 deletions