gccrs: ast: Add TokenStream collect function

gccrs: ast: Add TokenStream collect function

Add a function to TokenStream to collect in a single vector all tokens.

gcc/rust/ChangeLog:

	* ast/rust-ast-tokenstream.cc (TokenStream::collect_tokens): Add
	getter.
	(TokenStream::go): Rename function.
	(TokenStream::visit): Likewise.
	* ast/rust-ast-tokenstream.h: Add collect prototype.

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