attach and detach accessibility tree root element (#4382)

Author: meganrogge

src/browser/AccessibilityManager.ts

@@ -57,6 +57,7 @@ export class AccessibilityManager extends Disposable {
   ) {
     super();
     this._accessibilityTreeRoot = document.createElement('div');
+    this._terminal.element?.insertAdjacentElement('afterbegin', this._accessibilityTreeRoot);
     this._accessibilityTreeRoot.classList.add('xterm-accessibility');
     this._accessibilityTreeRoot.tabIndex = 0;