[flang] Fix problems with passed-object arguments by deferring the

identification of their index in the dummy argument list,
simplifying their representation, completing the representation
of their actual arguments, and (while I'm here) resolving
calls to type-bound procedures whose bindings are known at
compilation time.

Button up class ActualArgument by making remaining data
members private and adding accessors & mutators.

Original-commit: flang-compiler/f18@5eb60ec41912b0963e41bbc1a3141164efcb7fbf
Reviewed-on: https://github.com/flang-compiler/f18/pull/855