Consider emitting warnings for uses of pointers that violate their bounds-safe interfaces

[secure-sw-dev-bot]

This issue was copied from checkedc/checkedc-clang#1159

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In the future, we may want to consider warning the user if we can detect that the user of a pointer with a bounds-safe interface does not satisfy its bounds-safe interface. For example:

void f(int *p : itype(_Array_ptr<int>),
       int *q : bounds(unknown),
       int *r : count(2),
       int *s : count(1),
       int *t : itype(_Ptr<int>)) {
  // p has implicit declared bounds of bounds(unknown). p should not be dereferenced.
  *p;

  // q has explicit declared bounds of bounds(unknown). This is ok.
  *q;

  // The bounds of s are too small for the declared bounds of r.
  // This could be a bug in the user's chosen itype bounds.
  r = s;

  // Pointer arithmetic is not allowed on _Ptrs. The could be a bug in the user's chosen itype.
  t = t + 1;
}