feat(combo-box): make ComboBox slottable (#1181)

Closes #1176

docs/src/COMPONENT_API.json

@@ -1639,7 +1639,14 @@
         }
       ],
       "moduleExports": [],
-      "slots": [],
+      "slots": [
+        {
+          "name": "__default__",
+          "default": true,
+          "fallback": "{itemToString(item)}",
+          "slot_props": "{ item: ComboBoxItem; index: number }"
+        }
+      ],
       "events": [
         {
           "type": "dispatched",

docs/src/pages/components/ComboBox.svx

@@ -18,6 +18,12 @@ items={[
   {id: "2", text: "Fax"}
   ]}  />
 
+### Custom slot
+
+Override the default slot to customize the display of each item. Access the item and index through the `let:` directive.
+
+<FileSource src="/framed/ComboBox/ComboBoxSlot" />
+
 ### Selected id
 
 <ComboBox titleText="Contact" placeholder="Select contact method"

docs/src/pages/framed/ComboBox/ComboBoxSlot.svelte

@@ -0,0 +1,29 @@
+<script>
+  import { ComboBox } from "carbon-components-svelte";
+</script>
+
+<ComboBox
+  titleText="Contact"
+  placeholder="Select contact method"
+  items="{[
+    { id: '0', text: 'Slack' },
+    { id: '1', text: 'Email' },
+    { id: '2', text: 'Fax' },
+  ]}"
+  let:item
+  let:index
+>
+  <div>
+    <strong>{item.text}</strong>
+  </div>
+  <div>
+    id: {item.id} - index:
+    {index}
+  </div>
+</ComboBox>
+
+<style>
+  :global(.bx--list-box__menu-item, .bx--list-box__menu-item__option) {
+    height: auto;
+  }
+</style>