rustc_hir_analysis: fix generics_of ICE on unresolved const arguments

[InvalidPathException]

Fixes #148838

Root cause:
generics_of currently does not handle hir::Node::ConstArg so defaulted const args nested inside const paths try to inherit generics from the wrong place and trigger ICE.

Symptom:
#148838 ICE

Fix

Handle Node::ConstArg, in fact, similar logic already exists although it is in another branch and slightly more complex, not sure if there is a more elegant way:

rust/compiler/rustc_hir_analysis/src/collect/generics_of.rs

Lines 76 to 90 in 2636cb4

	// FIXME(#43408) always enable this once `lazy_normalization` is
	// stable enough and does not need a feature gate anymore.
	Node::AnonConst(_) => {
	let parent_did = tcx.parent(def_id.to_def_id());
	debug!(?parent_did);
	let mut in_param_ty = false;
	for (_parent, node) in tcx.hir_parent_iter(hir_id) {
	if let Some(generics) = node.generics() {
	let mut visitor = AnonConstInParamTyDetector { in_param_ty: false, ct: hir_id };
	in_param_ty = visitor.visit_generics(generics).is_break();
	break;
	}
	}

Testing:
1 more test case const-arg-unresolved.rs

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