gccrs: ast: Rename TokenStream in the AST module

gccrs: ast: Rename TokenStream in the AST module

Rename the TokenStream class to TokenCollector as it may induce errors
in the future as it is not a tokenstream as defined by the rust
interface. Furthermore this change match more closely the actual behavior
of the class.

gcc/rust/ChangeLog:

	* ast/rust-ast-tokenstream.cc (TokenStream::TokenStream): Rename
	TokenStream to TokenCollector.
	(TokenCollector::TokenCollector): Likewise.
	(TokenStream::collect_tokens): Likewise.
	(TokenCollector::collect_tokens): Likewise.
	(TokenStream::collect): Likewise.
	(TokenCollector::collect): Likewise.
	(TokenStream::visit): Likewise.
	(TokenCollector::visit): Likewise.
	(TokenStream::visit_items_joined_by_separator): Likewise.
	(TokenCollector::visit_items_joined_by_separator): Likewise.
	(TokenStream::visit_as_line): Likewise.
	(TokenCollector::visit_as_line): Likewise.
	(TokenStream::visit_items_as_lines): Likewise.
	(TokenCollector::visit_items_as_lines): Likewise.
	(TokenStream::visit_items_as_block): Likewise.
	(TokenCollector::visit_items_as_block): Likewise.
	(TokenStream::trailing_comma): Likewise.
	(TokenCollector::trailing_comma): Likewise.
	(TokenStream::newline): Likewise.
	(TokenCollector::newline): Likewise.
	(TokenStream::indentation): Likewise.
	(TokenCollector::indentation): Likewise.
	(TokenStream::increment_indentation): Likewise.
	(TokenCollector::increment_indentation): Likewise.
	(TokenStream::decrement_indentation): Likewise.
	(TokenCollector::decrement_indentation): Likewise.
	(TokenStream::visit_closure_common): Likewise.
	(TokenCollector::visit_closure_common): Likewise.
	(TokenStream::visit_loop_common): Likewise.
	(TokenCollector::visit_loop_common): Likewise.
	(TokenStream::visit_function_common): Likewise.
	(TokenCollector::visit_function_common): Likewise.
	* ast/rust-ast-tokenstream.h (class TokenStream): Likewise.
	(class TokenCollector): Likewise.
	* rust-session-manager.cc (Session::dump_tokenstream): Rename
	token vector for clearer intent.

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