Unable to infer base of key path from other arguments in code completion

[ahoppen]

The following new test case fails after #69742

// RUN: %batch-code-completion

struct Test {
    var currentHeight: Int

    func subscribeToKeyboardEvents() {
      objectAndKeyPath(object: self, keyPath: \.#^COMPLETE^#)
    }
}

func objectAndKeyPath<Root, Input>(object: Root, keyPath: WritableKeyPath<Root, Input>) {}

// COMPLETE: Decl[InstanceVar]/CurrNominal:      currentHeight[#Int#]; name=currentHeight