feat(components): add ComboBox

Closes #12

src/components/ComboBox/ComboBox.Story.svelte

@@ -0,0 +1,53 @@
+<script>
+  import Layout from '../../internal/ui/Layout.svelte';
+  import ToggleSmall from '../ToggleSmall';
+  import Button from '../Button';
+  import ComboBox from './ComboBox.svelte';
+
+  let items = [
+    { id: 'option-0', text: 'Option 1' },
+    { id: 'option-1', text: 'Option 2' },
+    { id: 'option-2', text: 'Option 3' },
+    { id: 'option-3', text: 'Option 4' },
+    {
+      id: 'option-4',
+      text: 'An example option that is really long to show what should be done to handle long text'
+    }
+  ];
+
+  let toggled = false;
+  let value = undefined;
+  let selectedIndex = -1;
+
+  function shouldFilterItem(item, value) {
+    if (!toggled || !value) {
+      return true;
+    }
+
+    return item.text.toLowerCase().includes(value.toLowerCase());
+  }
+</script>
+
+<Layout>
+  <p>Currently, this component does not support items as slots.</p>
+  <p>
+    <code>items</code>
+    must be an array of objects; mandatory fields are `id` and `text`.
+  </p>
+  <pre style="margin-top: 1rem;">
+    <code>{'items = Array<{ id: string; text: string; }>'}</code>
+  </pre>
+  <div style="margin-top: 2rem;">
+    <ToggleSmall labelText="Enable filtering" bind:toggled />
+    <Button
+      size="small"
+      on:click={() => {
+        selectedIndex = 1;
+      }}>
+      Set item to 'Option 2'
+    </Button>
+  </div>
+  <div style="width: 300px; margin-top: 2rem;">
+    <ComboBox {...$$props} id="combobox" bind:value bind:selectedIndex {items} {shouldFilterItem} />
+  </div>
+</Layout>