Check that constructor initializers for pointer fields are null-safe.

Nullable values should not passed to fields marked nonnull.
For example:
```
int * _Nullable makeNullable();
struct Foo {
  int * _Nonnull ptr_nonnull;
  Foo(): ptr_nonnull(makeNullable); // unsafe
};
```

PiperOrigin-RevId: 475349613
diff --git a/nullability_verification/pointer_nullability_matchers.h b/nullability_verification/pointer_nullability_matchers.h
index 0ab6e53..0dfa3c0 100644
--- a/nullability_verification/pointer_nullability_matchers.h
+++ b/nullability_verification/pointer_nullability_matchers.h
@@ -23,6 +23,7 @@
 ast_matchers::internal::Matcher<Stmt> isCallExpr();
 ast_matchers::internal::Matcher<Stmt> isPointerReturn();
 ast_matchers::internal::Matcher<Stmt> isConstructExpr();
+ast_matchers::internal::Matcher<CXXCtorInitializer> isCtorMemberInitializer();
 
 }  // namespace nullability
 }  // namespace tidy