gccrs: Make AttributeParser rely more on Parser

gccrs: Make AttributeParser rely more on Parser

gcc/rust/ChangeLog:

	* ast/rust-ast.cc (AttributeParser::parse_meta_item_inner):
	Handle removal of AttributeParser-specific functions.
	(AttributeParser::parse_path_meta_item): Likewise.
	(AttributeParser::parse_meta_item_seq): Likewise.
	(AttributeParser::parse_meta_item_lit): Likewise.
	(AttributeParser::parse_literal): Remove function.
	(AttributeParser::parse_simple_path): Likewise.
	(AttributeParser::parse_simple_path_segment): Likewise.
	(AttributeParser::peek_token): Likewise.
	(AttributeParser::skip_token): Likewise.
	* ast/rust-macro.h (AttributeParser::parse_simple_path):
	Likewise.
	(AttributeParser::parse_simple_path_segment): Likewise.
	(AttributeParser::parse_literal): Likewise.
	(AttributeParser::peek_token): Likewise.
	(AttributeParser::skip_token): Likewise.
	* parse/rust-parse.h (Parser): Make AttributeParser a friend
	class.

Signed-off-by: Owen Avery <powerboat9.gamer@gmail.com>