gccrs: Support type resolution on super traits on dyn objects

gccrs: Support type resolution on super traits on dyn objects

When checking if specified bounds satisfy other bounds we must lookup the
super traits. To finish the support for super traits we need to redo the
computation of method addresses to support super traits.

Addresses #914

gcc/rust/ChangeLog:

	* backend/rust-compile.cc: Add note about missing support for super
	traits.
	* typecheck/rust-tyty.cc (BaseType::satisfies_bound): New function.
	(BaseType::bounds_compatible): New function.
	(DynamicObjectType::get_object_items): New function.
	* typecheck/rust-hir-trait-ref.h: Use new API to perform type resolution
	on dyn objects.