feat(tree-view): make node slottable (#1843)

Closes #1660

docs/src/pages/framed/TreeView/TreeViewSlot.svelte

@@ -0,0 +1,61 @@
+<script>
+  import { TreeView } from "carbon-components-svelte";
+
+  let activeId = 0;
+  let selectedIds = [0, 7, 9];
+  let children = [
+    { id: 0, text: "AI / Machine learning" },
+    {
+      id: 1,
+      text: "Analytics",
+      children: [
+        {
+          id: 2,
+          text: "IBM Analytics Engine",
+          children: [
+            { id: 3, text: "Apache Spark" },
+            { id: 4, text: "Hadoop" },
+          ],
+        },
+        { id: 5, text: "IBM Cloud SQL Query" },
+        { id: 6, text: "IBM Db2 Warehouse on Cloud" },
+      ],
+    },
+    {
+      id: 7,
+      text: "Blockchain",
+      children: [{ id: 8, text: "IBM Blockchain Platform" }],
+    },
+    {
+      id: 9,
+      text: "Databases",
+      children: [
+        { id: 10, text: "IBM Cloud Databases for Elasticsearch" },
+        { id: 11, text: "IBM Cloud Databases for Enterprise DB" },
+        { id: 12, text: "IBM Cloud Databases for MongoDB" },
+        { id: 13, text: "IBM Cloud Databases for PostgreSQL" },
+      ],
+    },
+    {
+      id: 14,
+      text: "Integration",
+      disabled: true,
+      children: [{ id: 15, text: "IBM API Connect", disabled: true }],
+    },
+  ];
+</script>
+
+<TreeView
+  labelText="Cloud Products"
+  activeId="{activeId}"
+  selectedIds="{selectedIds}"
+  children="{children}"
+  let:node
+>
+  <span
+    style:color="{node.selected ? "var(--cds-interactive-04)" : "inherit"}"
+    style:text-decoration="{node.disabled ? "inherit" : "underline"}"
+  >
+    {node.text} (id: {node.id})
+  </span>
+</TreeView>