[flang] Correct handling of non-default lower bounds in ASSOCIATE with named constants

Work through several issues with LBOUND() and UBOUND() of ASSOCIATE
construct entities that have been associated with named constants or
subobjects of named constants that are sporting non-default lower bounds.
Sometimes the non-default lower bounds matter, sometimes they don't.
Add a fairly exhaustive test to work through the possibilities.

Differential Revision: https://reviews.llvm.org/D156756