Warn for generic declared return types without (?)

[mppf]

For https://github.com/Cray/chapel-private/issues/5229 / https://github.com/Cray/chapel-private/issues/4736#issuecomment-1666320252

Continuing #22745 and #23291, this PR adds a warning for routines declared with a generic return type that does not include (?). Note that we already have a number of problems using domain or domain(?) as a return or variable type (#23355, #23357, #23358); as a result domain(?) cannot currently be used as a declared return type.

While there, this PR adds checking to fix #23346 by making (?) on a concrete formal type into a compilation error. It also adds testing for the variable and return type cases to make sure that they also result in a compilation error.

For example:

record R { type t; }

proc a() : R { // warning
  return new R(int);
}
a();

proc b() : R(?) { // OK
  return new R(int);
}
b();

proc returnGenericType() type { return R; }

proc c() : returnGenericType() { // warning
  return new R(int);
}
c();

proc d() : returnGenericType()(?) { // OK
  return new R(int);
}
d();

Reviewed by @vasslitvinov and @lydia-duncan - thanks!

• full comm=none testing
• full gasnet testing

[lydia-duncan]

Test changes all look reasonable to me, too!