jsdialog: add id to treeview entries to preserve focus across updates

Treeview rows had no id attribute. When pressing Enter on a treeview
entry, core triggers _updateWidgetImpl.

That method saves document.activeElement.id, rebuilds the widget, then
tries to restore focus by finding an element with that the old id. Since
the button had no id the fallback of sending focus to the document body
happens.

Use the same fix and pattern as:

  commit 3f985cb
  Date:   Tue Jun 17 13:23:38 2025 +0530

      iconview: added support for keyboard navigation after click

Signed-off-by: Caolán McNamara <caolan.mcnamara@collabora.com>
Change-Id: Ie37a93dc52d41668169a8c03bcae23c82ad9c710

Author: caolanm

browser/src/control/jsdialog/Widget.TreeView.ts

@@ -367,6 +367,9 @@ class TreeViewControl {
 			parent,
 		);
 		this._rows.set(String(entry.row), tr);
+
+		//id is needed to find the element to regain focus after widget is updated. see updateWidget in Control.JSDialogBuilder.js
+		tr.id = data.id + '_' + entry.row;
 		tr.setAttribute('level', String(level));
 		(tr as any)._row = entry.row;
 		const rowRole =