fix: A few things for the plugin.

This exposes FocusableTreeTraverser for the plugin's use. It also fixes
a few callback issues with FocusManager that were missed in RaspberryPiFoundation#8909.

Author: BenHenning

core/blockly.ts

@@ -111,6 +111,9 @@ import {
   ReturnEphemeralFocus,
   getFocusManager,
 } from './focus_manager.js';
+import {
+  FocusableTreeTraverser,
+} from './utils/focusable_tree_traverser.js';
 import {CodeGenerator} from './generator.js';
 import {Gesture} from './gesture.js';
 import {Grid} from './grid.js';
@@ -527,6 +530,7 @@ export {
   FlyoutMetricsManager,
   FlyoutSeparator,
   FocusManager,
+  FocusableTreeTraverser,
   CodeGenerator as Generator,
   Gesture,
   Grid,

core/focus_manager.ts

@@ -247,7 +247,7 @@ export class FocusManager {
 
     const prevNode = this.focusedNode;
     const prevTree = prevNode?.getFocusableTree();
-    if (prevNode && prevTree !== nextTree) {
+    if (prevNode) {
       this.passivelyFocusNode(prevNode, nextTree);
     }
 
@@ -374,7 +374,9 @@ export class FocusManager {
     // node's focusable element (which *is* allowed to be invisible until the
     // node needs to be focused).
     this.lockFocusStateChanges = true;
-    node.getFocusableTree().onTreeFocus(node, prevTree);
+    if (node.getFocusableTree() !== prevTree) {
+      node.getFocusableTree().onTreeFocus(node, prevTree);
+    }
     node.onNodeFocus();
     this.lockFocusStateChanges = false;
 
@@ -399,11 +401,15 @@ export class FocusManager {
     nextTree: IFocusableTree | null,
   ): void {
     this.lockFocusStateChanges = true;
-    node.getFocusableTree().onTreeBlur(nextTree);
+    if (node.getFocusableTree() !== nextTree) {
+      node.getFocusableTree().onTreeBlur(nextTree);
+    }
     node.onNodeBlur();
     this.lockFocusStateChanges = false;
 
-    this.setNodeToVisualPassiveFocus(node);
+    if (node.getFocusableTree() !== nextTree) {
+      this.setNodeToVisualPassiveFocus(node);
+    }
   }
 
   /**