Move role=document to xterm element

Feedback in microsoft/vscode#98918 said this could improve the UX on
screen readers

src/browser/AccessibilityManager.ts

@@ -57,7 +57,6 @@ export class AccessibilityManager extends Disposable {
 
     this._rowContainer = document.createElement('div');
     this._rowContainer.classList.add('xterm-accessibility-tree');
-    this._rowContainer.setAttribute('role', 'document');
     this._rowElements = [];
     for (let i = 0; i < this._terminal.rows; i++) {
       this._rowElements[i] = this._createAccessibilityTreeNode();

src/browser/Terminal.ts

@@ -383,6 +383,7 @@ export class Terminal extends CoreTerminal implements ITerminal {
     this.element.classList.add('terminal');
     this.element.classList.add('xterm');
     this.element.setAttribute('tabindex', '0');
+    this.element.setAttribute('role', 'document');
     parent.appendChild(this.element);
 
     // Performance: Use a document fragment to build the terminal