gccrs: Fix recusive type query and nullptr on type path

This was a small fix to sort out the segfault to check for nullptr on the
TypePath cases for query type. But when this happened opened up a few bugs
that were hidden under the carpet namely: compile/issue-2905-{1,2}.rs which
has a recursive type query which needs to ne handled but now and error
message is being output for the type path. This happens because we start
resolving a generic struct:

  struct Wierd<T>(A<(T,)>);

So the child field A is also generic and the generic argument of the tuple
of T needs to be applied to this generic field. This causes a chunk of
code to do bounds checking to ensure the bounds are ok, this is also
something that probably might change as generic types will have the bounds
secified anyway but thats besides the case right now. So once this bounds
checking occurs we endup looking at the impl block for Wierd<i32> which is
also grand but we still havent finished resolving the parent type of Wierd
which is recusive. But the query type system needs to check for that.

The other issue was: compile/issue-3022.rs which is a resolution issue:

  impl<T: Foo<U>, U> Foo<U> for Bar<T, U>

The bound of Foo<T> is added to T before U is resolved but this was hidden
before the new error message was added. So now we have a generic
arguements handler being used correctly all over the code base apart from
1 last case for Traits but we will deal with that later. This handles the
case by setting up the type parameters upfront then sorting out their
bounds.

Fixes Rust-GCC#3625

gcc/rust/ChangeLog:

	* typecheck/rust-hir-trait-resolve.cc (TraitResolver::resolve_trait): new argument
	* typecheck/rust-hir-type-check-base.cc (TypeCheckBase::TypeCheckBase): new helper
	* typecheck/rust-hir-type-check-base.h: new helper prototype
	* typecheck/rust-hir-type-check-implitem.cc (TypeCheckTopLevelExternItem::visit):
	remove comment out code
	* typecheck/rust-hir-type-check-path.cc (TypeCheckExpr::resolve_root_path): check for null
	* typecheck/rust-hir-type-check-type.cc (TypeCheckType::resolve_root_path): likewise
	(TypeResolveGenericParam::Resolve): new args
	(TypeResolveGenericParam::ApplyAnyTraitBounds): new helper
	(TypeResolveGenericParam::apply_trait_bounds): new field
	(TypeResolveGenericParam::visit): update
	* typecheck/rust-hir-type-check-type.h: new args
	* typecheck/rust-hir-type-check.cc (TraitItemReference::get_type_from_fn): reuse helper
	* typecheck/rust-type-util.cc (query_type): check for recursive query
	* typecheck/rust-tyty-subst.cc (SubstitutionParamMapping::SubstitutionParamMapping):
	remove const
	(SubstitutionParamMapping::get_generic_param): likewise
	* typecheck/rust-tyty-subst.h: likewise
	* typecheck/rust-tyty-variance-analysis.cc (GenericTyVisitorCtx::process_type): likewise

gcc/testsuite/ChangeLog:

	* rust/compile/issue-3625.rs: New test.

Signed-off-by: Philip Herron <herron.philip@googlemail.com>

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