fix(overlays): move prepareOverlay to connectedCallback

For custom elements builds, overlays cannot use hasAttribute() in the constructor, so moving it to connectedCallback instead.

core/src/components/picker/picker.tsx

@@ -100,7 +100,7 @@ export class Picker implements ComponentInterface, OverlayInterface {
    */
   @Event({ eventName: 'ionPickerDidDismiss' }) didDismiss!: EventEmitter<OverlayEventDetail>;
 
-  constructor() {
+  connectedCallback() {
     prepareOverlay(this.el);
   }