Fortran: Move caf_get-rewrite to coarray.cc [PR107635]

Fortran: Move caf_get-rewrite to coarray.cc [PR107635]

Add a rewriter to keep all expression tree that is not optimization
together.  At the moment this is just a move from resolve.cc, but will
be extended to handle more cases where rewriting the expression tree may
be easier.  The first use case is to extract accessors for coarray
remote image data access.

gcc/fortran/ChangeLog:

	PR fortran/107635
	* Make-lang.in: Add coarray.cc.
	* coarray.cc: New file.
	* gfortran.h (gfc_coarray_rewrite): New procedure.
	* parse.cc (rewrite_expr_tree): Add entrypoint for rewriting
	expression trees.
	* resolve.cc (gfc_resolve_ref): Remove caf_lhs handling.
	(get_arrayspec_from_expr): Moved to rewrite.cc.
	(remove_coarray_from_derived_type): Same.
	(convert_coarray_class_to_derived_type): Same.
	(split_expr_at_caf_ref): Same.
	(check_add_new_component): Same.
	(create_get_parameter_type): Same.
	(create_get_callback): Same.
	(add_caf_get_intrinsic): Same.
	(resolve_variable): Remove caf_lhs handling.

libgfortran/ChangeLog:

	* caf/single.c (_gfortran_caf_finalize): Free memory preventing
	leaks.
	(_gfortran_caf_get_by_ct): Fix constness.
	* caf/libcaf.h (_gfortran_caf_register_accessor): Fix constness.