[flang] Check for elemental finalizer when defined object has vector subscript

When a defined object is an array with a vector subscript, and it has a
finalizable type, it may have a final subroutine with a matching or
assumed rank dummy argument that cannot be called.  Unless there is
also a suitable elemental final subroutine, diagnose such a case
with an error message.

Differential Revision: https://reviews.llvm.org/D140131