[flang] Use passed-object dummy in distinguishability checks

Complete the checks for distinguishable specifics procedure in a generic
by considering any passed-object dummy arguments.

C1514 rule 3 is implemented and the checks for the other rules are
extended to consider the PASS attribute, including the concept of the
"effective" position of an argument in an argument list, computed by
ignoring passed-object arguments.

Add `pass` to `characteristics::DummyArgument` to mark each
passed-object dummy argument.

Change symbols to store the index of the passed-object dummy argument
rather than its symbol.

Check that specifics of a type-bound generic are distinguishable only
after all of the procedure bindings have been processed. They don't have
to be before the generic.

Original-commit: flang-compiler/f18@2751490f95fa5ca321c912330aca1091cdbc2f70
Reviewed-on: https://github.com/flang-compiler/f18/pull/567