Fill in some missing cases for bounds-safe interface assignments

[secure-sw-dev-bot]

This issue was copied from checkedc/checkedc-clang#813

---

This PR addresses issue #810 by filling in two missing cases for bounds-safe interface assignment compatibility:

1. Extend GetCheckedCInteropType to get the bounds-safe interface type for pointer dereferences and array subscripts
2. Allow assignment of an unchecked nt_array_ptr with a bounds-safe interface to a checked nt_array_ptr

Testing:

• Added Checked C tests to test the new assignment compatibility cases (PR #398)
• Passed manual testing on Windows
• Passed automated testing on Windows/Linux