[flang][hlfir] Emit hlfir.declare inside internal procedures

Captured variables inside internal procedure do not go though
Fortran::lower::instantiateVar because the specification expressions
should no be lowered again, and instead, all the information must be
taken from the host link argument.

There is nothing very special to do for HLFIR, but the hlfir.declare
should be emitted for the instantiated captured variable and mapped
to the symbol.

Differential Revision: https://reviews.llvm.org/D143481