[flang][hlfir] Enable lowering and passing of allocatables and pointers.

Adds support for:
- referencing a whole allocatable/pointer symbol
- passing allocatable/pointer in a call

This required update in HLFIRTools.cpp helpers so that the
raw address, extents, lower bounds, and type parameters of a
fir.box/fir.class can be extracted.
This is required because in hlfir lowering, dereferencing a
pointer/alloc is only doing the fir.load fir.box part, and the
helpers have to be able to reason about that fir.box without the
help of a "fir::FortranVariableOpInterface".

Missing:
- referencing part of allocatable/pointer (will need to update
  Designator lowering to dereference the pointer/alloc). Same
  for whole allocatable and pointer components.
- allocate/deallocate/pointer assignment statements.
- Whole allocatable assignment.
- Lower inquires.

Differential Revision: https://reviews.llvm.org/D142043