PR25230, dwarf2.c per file stash

PR25230, dwarf2.c per file stash

This is just moving things around, in preparation for parsing alt
file debug_info.

	PR 25230
	* dwarf2.c (struct dwarf2_debug_file): New struct.
	(struct dwarf2_debug): Delete fields now in dwarf2_debug_file.
	Add f, alt fields.
	(struct comp_unit): Add file field.
	(read_indirect_string, read_indirect_line_string): Adjust to suit.
	(read_alt_indirect_string, read_alt_indirect_ref): Likewise.
	(read_debug_ranges, find_abstract_instance, read_rangelist): Likewise.
	(_bfd_dwarf2_stash_syms, place_sections): Likewise.
	(stash_maybe_update_info_hash_tablse): Likewise.
	(stash_verify_info_hash_table): Likewise.
	(_bfd_dwarf2_slurp_debug_info): Likewise.
	(_bfd_dwarf2_find_symbol_bias): Likewise.
	(_bfd_dwarf2_find_nearest_line): Likewise.
	(_bfd_dwarf2_cleanup_debug_info): Likewise.
	(read_abbrevs): Add file param and adjust.  Update calls.
	(stash_comp_unit): Likewise.
	(decode_line_info): Delete stash param and adjust.  Update calls.
	(comp_unit_find_nearest_line): Likewise.
	(comp_unit_maybe_decode_line_info): Likewise.
	(comp_unit_find_line): Likewise.
	(parse_comp_unit): Add file and info_ptr param and adjust.  Update
	calls.