Feat：非富文本模式下节点文本编辑框增加类名，方便覆盖样式

simple-mind-map/src/core/render/TextEdit.js

@@ -216,6 +216,7 @@ export default class TextEdit {
     this.registerTmpShortcut()
     if (!this.textEditNode) {
       this.textEditNode = document.createElement('div')
+      this.textEditNode.classList.add('smm-node-edit-wrap')
       this.textEditNode.style.cssText = `position:fixed;box-sizing: border-box;background-color:#fff;box-shadow: 0 0 20px rgba(0,0,0,.5);padding: ${this.textNodePaddingY}px ${this.textNodePaddingX}px;margin-left: -5px;margin-top: -3px;outline: none; word-break: break-all;`
       this.textEditNode.setAttribute('contenteditable', true)
       this.textEditNode.addEventListener('keyup', e => {