gccrs: Initial Type resolution for closures

gccrs: Initial Type resolution for closures

gcc/rust/ChangeLog:

	* hir/tree/rust-hir-expr.h: Add `get_params` method.
	* typecheck/rust-hir-type-check-expr.cc (TypeCheckExpr::visit): Typecheck closure nodes.
	(TypeCheckExpr::resolve_fn_trait_call): New function.
	* typecheck/rust-hir-type-check-expr.h: Declare `resolve_fn_trait_call` and
	`resolve_possible_fn_trait_call_method_name`.
	* typecheck/rust-hir-type-check.h: Declare `get_context_type`.
	* typecheck/rust-tyctx.cc (TypeCheckContextItem::get_context_type): New function.
	* typecheck/rust-tyty-cmp.h: Visit closures properly.
	* typecheck/rust-tyty-rules.h: Likewise.
	* typecheck/rust-tyty.cc (BaseType::bounds_compatible): Add commented out assertin.
	(ClosureType::as_string): Implement it.
	(ClosureType::clone): Fix closure cloning.
	(ClosureType::setup_fn_once_output): New function.
	* typecheck/rust-tyty.h: Improve `ClosureType` class and declare `setup_fn_once_output`.