gccrs: expand: Add call to outer attributes stubs

gccrs: expand: Add call to outer attributes stubs

Add call to outer attribute expansion stub on required types.

gcc/rust/ChangeLog:

	* expand/rust-expand-visitor.cc (ExpandVisitor::expand_struct_fields):
	Add call to expand structu fields.
	(ExpandVisitor::expand_function_params): Add call to expand
	function parameters.
	(ExpandVisitor::expand_closure_params): Add call to expand
	closure parameters.
	(ExpandVisitor::visit): Add calls for item outer attribute
	expansions.

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