C++: Test C++20 implicit array sizes.

[calumgrant]

Adds tests for C++ 20 implicit new array sizes. Also reviewed the QL libraries and did not find any use of NewArrayExpr.getExtent() that would benefit from using getArraySize() instead.

[jketema]

Do we use getAllocatedType().(ArrayType).getArraySize() directly in places where we should actually be using the predicate introduced here?

[calumgrant]

Do we use getAllocatedType().(ArrayType).getArraySize() directly in places where we should actually be using the predicate introduced here?

I can't find any.

[jketema]

The change should go in cpp/ql/lib/change-notes (it's a library change, not a query change). That should also fix the error you're getting now.

[jketema]

Do we use getAllocatedType().(ArrayType).getArraySize() directly in places where we should actually be using the predicate introduced here?

I can't find any.

I'm finding cpp/leap-year/unsafe-array-for-days-of-the-year and cpp/bad-strncpy-size. However, it's better to create an issue for follow-up work then to possibly change those queries as part of this PR.

[jketema]

LGTM.