[flang][hlfir] Lower associate construct to HLFIR

- always use genExprAddr when lowering to HLFIR: it does not create
  temporary for array sections without vector subscripts, so there is
  no need to have custom logic.

- update mangling to deal with AssocDetailsEntity. Their name is
  required in HLFIR so that it can be added to the hlfir.declare
  that is created for the selector once it is lowered. This should
  allow getting debug info for selector when debug info are generated
  from hlfir.declare.

The rest of associate construct lowering is unchanged and shared with
the current lowering.

This patch also enables select type lowering to work properly, but some
other todos (mainly about parent component references) prevents porting
the tests for now, so this will be done later.

Differential Revision: https://reviews.llvm.org/D144740