suppression: Factorize out is_data_member_offset_in_range

suppression: Factorize out is_data_member_offset_in_range

In preparation of subsequent changes, this patch factorizes a function
is_data_member_offset_in_range() out of
type_suppression::suppression().  This is useful to determine if a
data member offset is within an "offset range" expressed by the
type_suppression::insertion_range type.

This function is useful to implement the
offset_of_first_data_member_regexp and
offset_of_last_data_member_regexp properties to come in subsequent
patches.

Please note that is_data_member_offset_in_range works on data members
of unions and classes, not just on classes like what the original code
of inside type_suppression::suppresses_diff was doing.

This patch should not have any functional impact on the code.

	* include/abg-fwd.h (get_last_data_member)
	(get_next_data_member_offset): Declare functions.
	* src/abg-ir.cc (get_next_data_member): Add an overload for
	class_or_union and write the overload for class_or_union_sptr in
	term of the former.
	(get_last_data_member): Add overloads form class_or_union& and
	class_or_union*.  Write the overload for class_or_union_sptr in
	terms of the one for class_or_union*.
	(get_next_data_member_offset): Add an overload for
	class_or_union* and write the overload for class_or_union_sptr in
	terms of the former.
	* include/abg-suppression.h
	(type_suppression::insertion_range::eval_boundary): Take a
	class_or_union* for the context, as opposed to a class_decl_sptr.
	This makes this static function work for unions as well.
	(is_data_member_offset_in_range): Declare new function.
	* src/abg-suppression.cc (type_suppression::suppression_diff):
	Factorize ...
	(is_data_member_offset_in_range): ... this function out.
	(type_suppression::insertion_range::eval_boundary): Adjust this to
	make it take a class_or_union* rather than a class_decl_sptr.

Signed-off-by: Dodji Seketeli <dodji@redhat.com>