Fortran: Fix some problems with SELECT TYPE selectors [PR104625].

Fortran: Fix some problems with SELECT TYPE selectors [PR104625].

2023-10-27  Paul Thomas  <pault@gcc.gnu.org>

gcc/fortran
	PR fortran/104625
	* expr.cc (gfc_check_vardef_context): Check that the target
	does have a vector index before emitting the specific error.
	* match.cc (copy_ts_from_selector_to_associate): Ensure that
	class valued operator expressions set the selector rank and
	use the rank to provide the associate variable with an
	appropriate array spec.
	* resolve.cc (resolve_operator): Reduce stacked parentheses to
	a single pair.
	(fixup_array_ref): Extract selector symbol from parentheses.

gcc/testsuite/
	PR fortran/104625
	* gfortran.dg/pr104625.f90: New test.
	* gfortran.dg/associate_55.f90: Change error check.