Improve type definitions for the viewer

This commit improves compatibility of the viewer code with TypeScript by including missing type imports/definitions and correcting existing ones

web/base_tree_viewer.js

@@ -43,14 +43,14 @@ class BaseTreeViewer {
   }
 
   /**
-   * @private
+   * @protected
    */
   _dispatchEvent(count) {
     throw new Error("Not implemented: _dispatchEvent");
   }
 
   /**
-   * @private
+   * @protected
    */
   _bindLink(element, params) {
     throw new Error("Not implemented: _bindLink");
@@ -71,7 +71,9 @@ class BaseTreeViewer {
   /**
    * Prepend a button before a tree item which allows the user to collapse or
    * expand all tree items at that level; see `_toggleTreeItem`.
-   * @private
+   * @param {HTMLDivElement} div
+   * @param {boolean|object} [hidden]
+   * @protected
    */
   _addToggleButton(div, hidden = false) {
     const toggler = document.createElement("div");