Generalize assignment compatibility for bounds-safe interfaces

[kkjeer]

The current rules for assignment compatibility of expressions involving bounds-safe interfaces are missing two cases.

The first case is related to assignments involving nested pointers (see #797). GetCheckedCInteropType should be extended to handle dereferences and pointer arithmetic.

The second case is related to assignments of an unchecked pointer with an _Nt_array_ptr bounds-safe interface to an _Nt_array_ptr variable (see #806). The type checker should check the bounds-safe interface of the unchecked pointer in this case.

[kkjeer]

This issue tracks the implementation of the spec updates described in microsoft/checkedc/#397.

[kkjeer]

This issue was fixed in the 2020-07-31 release of Checked C.