如何在lwc中获取lightning输入富文本中的光标位置？

<lightning-input-rich-text
    value={richTextValue}
    onchange={handleRichTextChange}
></lightning-input-rich-text>

import { LightningElement, track } from 'lwc';

export default class MyComponent extends LightningElement {
    @track richTextEditor;

    handleRichTextChange(event) {
        this.richTextEditor = event.target;
    }
}

getCursorPosition() {
    const selection = this.richTextEditor.getSelection();
    const range = selection.getRangeAt(0);
    const offset = range.startOffset;
    console.log('光标位置：', offset);
}

<lightning-button label="获取光标位置" onclick={getCursorPosition}></lightning-button>