Add leading icon slot to expansion panel and fix left-chevron property (#24635)

* Add leading icon slot to expansion panel and fix left chevron

* Update components

gallery/src/pages/components/ha-expansion-panel.ts

@@ -1,4 +1,4 @@
-import { mdiPacMan } from "@mdi/js";
+import { mdiLightbulbOn, mdiPacMan } from "@mdi/js";
 import type { TemplateResult } from "lit";
 import { css, html, LitElement } from "lit";
 import { customElement } from "lit/decorators";
@@ -125,6 +125,23 @@ const SAMPLES: {
       `;
     },
   },
+  {
+    template(slot, leftChevron) {
+      return html`
+        <ha-expansion-panel
+          slot=${slot}
+          .leftChevron=${leftChevron}
+          header="Attr Header with actions"
+        >
+          <ha-svg-icon
+            slot="leading-icon"
+            .path=${mdiLightbulbOn}
+          ></ha-svg-icon>
+          ${SHORT_TEXT}
+        </ha-expansion-panel>
+      `;
+    },
+  },
 ];
 
 @customElement("demo-components-ha-expansion-panel")