fix(ui5-dialog): dialog focus trapping works again (#1213)

Author: vladitasev

packages/main/src/Dialog.hbs

@@ -1,6 +1,6 @@
 {{>include "./Popup.hbs"}}
 
-<span class="ui5-popup-frame">
+<span class="ui5-popup-frame" @focusin="{{_onfocusin}}">
 	<span id="{{_id}}-firstfe" tabindex="0"></span>
 	<div style="{{zindex}}" class="ui5-dialog-root-parent {{classes.dialogParent}}">
 		<div tabindex="-1" aria-labelledby="{{headerId}}" role="dialog" aria-modal="true" class="ui5-popup-root ui5-dialog-root">

packages/main/src/Popup.js

@@ -385,7 +385,7 @@ class Popup extends UI5Element {
 		}
 	}
 
-	onfocusin(event) {
+	_onfocusin(event) {
 		this.preserveFocus(event, this.getPopupDomRef());
 	}