[flang] Disallow BOZ literal constants as output list items

[flang] Disallow BOZ literal constants as output list items

According to C7109, "A boz-literal-constant shall appear only as a
data-stmt-constant in a DATA statement, or where explicitly allowed in
16.9 as an actual argument of an intrinsic procedure."  This change
enforces that constraint for output list items.

I also added a general interface to determine if an expression is a BOZ
literal constant and changed all of the places I could find where it
could be used.

I also added a test.

This change stemmed from the following issue --
  https://gitlab-master.nvidia.com/fortran/f18-stage/issues/108

Differential Revision: https://reviews.llvm.org/D106893