gdb: add gdb_bfd_sections for range-based iteration

gdb: add gdb_bfd_sections for range-based iteration

I wanted to make a nicer / type-safe interface for
bfd_map_over_sections, avoiding the `void *` data parameter.

My first shot was to make a wrapper for bfd_map_over_sections,
gdb_bfd_map_over_sections that took a gdb::function_view.

However, I think that a range adapter gives nicer and simpler code, as a
simple for loop is easier to read than a callback / lambda function.  So
here it is, it uses next_iterator and next_adapter, so it's not much
code.

As an example, I ported maintenance_info_sections and friends to use it.
The maint_print_section_data type could probably be removed now, but I
didn't want to do too much in one patch.

gdb/ChangeLog:

	* gdb_bfd.h (gdb_bfd_section_iterator, gdb_bfd_section_range,
	gdb_bfd_sections): New.
	* maint.c (print_bfd_section_info): Change param type to
	maint_print_section_data.
	(print_objfile_section_info): Likewise.
	(print_bfd_section_info_maybe_relocated): Likewise.
	(maintenance_info_sections): Use gdb_bfd_sections.

Change-Id: Ib496f6b0a0eb7aadb10da1dd381304014d934ea0