Markdown editor auto-complete enhancement

[x2358473]

Describe the solution you'd like

#2773 的问题延续
问题1：
"- [ ] "这个标签回车后变成
" - "
问题2：

1. 这是一个列表
2. 这是一个列表
3. “如果我在这里再按一次Enter键应该删除 ‘3.’ 这个标签，但是我现在要手动删除它”

在v0.21.0中似乎并没有完全优化markdwon的语法。比如 - [ ] 这个标签，使用回车后只会重复 " - "这个，它后面的 " [ ] "标签还是丢失了，等于还是没作用。只有list标签有点作用，如 1. 2. 这种的回车会进行重复。
且markdown中如果回车重复上一行的标签后再次按回车是清除重复的标签的，目前的版本再次按回车键是直接生成了新的一行，上一行留一个空标签行在那里，我不知道是出于什么原因导致这些问题。但在早期的版本中这些是完整支持的。

en:
This problem doesn't seem to be fully optimized in v0.21.0. For example, the label - [ ] will only repeat " - " after using carriage return. The " [ ] " label after it is still lost, which means it still has no effect. Only the list tag has some effect, such as 1. 2. This type of carriage return will be repeated.
And in markdown, if you press Enter to repeat the label of the previous line and then press Enter again, the repeated labels will be cleared. In the current version, pressing Enter again will directly generate a new line, leaving an empty label line in the previous line. I Don't know what causes these problems. But in earlier versions these were fully supported.

Type of feature

User Experience (UX)

Additional context

个人感觉这个应用就是用来记录一些平常的事项，那么列表与 ”- [ ] “checkbox 这两个标签应该是比较常用到。在1.9的版本之前是完整支持markdown的上述语法，但是后面的就不支持了，而在0.21.0中优化只是进行了重复上一行的第一个字符，并不是重复标签，导致实际使用中，checkbox还是每次只能手动插入

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Issue is not in English. It has been translated automatically.

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Title: markdown syntax added