gccrs: Fix StructPattern type checking rejecting tuple struct scrutinee

gccrs: Fix StructPattern type checking rejecting tuple struct scrutinee

Previously, type checking of StructPattern will throw an error if it is used
to match against a tuple struct, even though it is possible to do so in rustc.

gcc/rust/ChangeLog:

	* typecheck/rust-hir-type-check-pattern.cc (visit(StructPattern)): Add type check
	support for StructPatterns matching against a TUPLE type ADT.
	* backend/rust-compile-pattern.cc(CompilePatternBindings::visit(StructPattern)):
	Update assert to allow TUPLE type ADTs.
	* hir/tree/rust-hir.cc (StructPatternField::as_string()): Improve info dumped.

Signed-off-by: Yap Zhi Heng <yapzhhg@gmail.com>