gccrs: collector: Store CollectItem instead of TokenPtr

gccrs: collector: Store CollectItem instead of TokenPtr

Store a custom type to differentiate formatting and metadata from data.

gcc/rust/ChangeLog:

	* ast/rust-ast-collector.cc (TokenCollector::collect_tokens):
	Filter tokens.
	(TokenCollector::visit_items_joined_by_separator): Change store
	call.
	(TokenCollector::visit_as_line): Likewise.
	(TokenCollector::visit_items_as_block): Likewise.
	(TokenCollector::trailing_comma): Likewise.
	(TokenCollector::visit): Likewise.
	(TokenCollector::visit_closure_common): Likewise.
	(TokenCollector::visit_function_common): Likewise.
	* ast/rust-ast-collector.h (class CollectItem): Add class to
	differentiate between formatting and raw data (tokens).

Signed-off-by: Pierre-Emmanuel Patry <pierre-emmanuel.patry@embecosm.com>