Move cursor render layer to browser

src/browser/services/CoreBrowserService.ts

@@ -0,0 +1,19 @@
+/**
+ * Copyright (c) 2019 The xterm.js authors. All rights reserved.
+ * @license MIT
+ */
+
+import { ICoreBrowserService } from './Services';
+
+export class CoreBrowserService implements ICoreBrowserService {
+  serviceBrand: any;
+
+  constructor(
+    private _textarea: HTMLTextAreaElement
+  ) {
+  }
+
+  public get isFocused(): boolean {
+    return document.activeElement === this._textarea && document.hasFocus();
+  }
+}