Ensure TupleStructPattern and TuplePattern have items

Ensure TupleStructPattern and TuplePattern have items

Note that instances of both classes which have been
moved from will have (items == nullptr).

gcc/rust/ChangeLog:

	* ast/rust-pattern.h
	(class TupleStructPattern): Assert that items != nullptr.
	(class TuplePattern): Likewise.
	(TupleStructPattern::has_items): Remove.
	(TuplePattern::has_tuple_pattern_items): Likewise.
	* parse/rust-parse-impl.h
	(Parser::parse_ident_leading_pattern):
	Prevent construction of TupleStructPattern with
	(items == nullptr).
	(Parser::parse_pattern_no_alt): Likewise.
	* ast/rust-ast-collector.cc
	(TokenCollector::visit): Remove usage of
	TupleStructPattern::has_items.
	* ast/rust-ast-visitor.cc
	(DefaultASTVisitor::visit): Likewise.
	* resolve/rust-early-name-resolver.cc
	(EarlyNameResolver::visit): Likewise.

gcc/testsuite/ChangeLog:

	* rust/compile/pattern-struct.rs: Fix test.

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