fix(popover): fire "click:outside" event when clicking sibling elements (#1570)

docs/src/pages/framed/Popover/WithButton.svelte

@@ -0,0 +1,37 @@
+<script>
+  import { Popover, Button } from "carbon-components-svelte";
+
+  let open = true;
+  let containerRef = null;
+</script>
+
+<div data-outline>
+  <div
+    bind:this="{containerRef}"
+    style:position="relative"
+    style:display="inline-block"
+  >
+    <Button on:click="{() => (open = !open)}">Click to open</Button>
+    <Popover
+      bind:open
+      align="bottom-left"
+      on:click:outside="{({ detail }) => {
+        console.log('on:click:outside');
+        if (!containerRef.contains(detail.target)) {
+          open = false;
+        }
+      }}"
+    >
+      <div style="padding: var(--cds-spacing-05)">Content</div>
+    </Popover>
+  </div>
+  <div>
+    <br />
+    Anim eu laboris veniam in est elit ullamco enim irure id. Lorem est culpa ex
+    in enim enim. Culpa quis incididunt magna officia et aliqua. Ullamco deserunt
+    aute enim cupidatat. Culpa quis enim sint sint anim qui irure exercitation labore
+    occaecat in reprehenderit proident. Nisi laborum ut et amet commodo amet ullamco
+    commodo non aliqua magna ad eu. Ad aliquip minim nostrud id enim elit velit ullamco
+    pariatur eu excepteur pariatur cillum.
+  </div>
+</div>