Re-work toHierarchy utility

Refactor `toHiearchy` to be more generic, performant

- Use callback to "pick" generic parent ID property instead of requiring that `pid` be hardcoded`
- Account for edge cases of an invalid parent ID
- Use Map to store node children for lookups
- Use one pass instead of removing empty nodes at the very end
- DX: use generics to type `toHierarchy`
- Make `toHierarchy` even more generic (reusable with `RecursiveList`)

Co-Authored-By: Bram <bramhavers@gmail.com>

tests/RecursiveList/RecursiveList.test.svelte

@@ -0,0 +1,28 @@
+<script lang="ts">
+  import { RecursiveList } from "carbon-components-svelte";
+
+  const nodes = [
+    {
+      text: "Item 1",
+      nodes: [
+        {
+          text: "Item 1a",
+          nodes: [{ html: "<h5>HTML content</h5>" }],
+        },
+      ],
+    },
+    {
+      text: "Item 2",
+      nodes: [
+        { href: "https://svelte.dev/" },
+        {
+          href: "https://svelte.dev/",
+          text: "Link with custom text",
+        },
+      ],
+    },
+    { text: "Item 3" },
+  ];
+</script>
+
+<RecursiveList type="ordered" {nodes} />