fix(filter/highlight): avoid escaping curly bracket when highlight & prismjs disabled

[curbengh]

What does it do?

Fixes #4482

How to test

git clone -b unescape-curly-bracket https://github.com/curbengh/hexo.git
cd hexo
npm install
npm test

Screenshots

Pull request tasks

• Add test cases for the changes.
• Passed the CI test.

[coveralls]

Coverage remained the same at 98.296% when pulling b7e1150 on curbengh:unescape-curly-bracket into ebc9008 on hexojs:master.

[curbengh]

{% asset_img 'icon.jpg' %}

{% codeblock lang:objc wrap:true title:bob %}
[rectangle setX: 10 y: 10 width: 20 height: 20];
{% endcodeblock %}

```js caption
console.log('foo')
```

<br>

``` foo
lorem ipsum dolor
```

![hello](https://via.placeholder.com/100x100)

```markdown
{% meting "000PeZCQ1i4XVs" "tencent" "artist" "theme:#3F51B5" "mutex:true" "preload:auto" %}
```

``` js
{% asset_img 'icon.jpg' %}
```

`{% test %}`

before:

after:

[SukkaW]

LGTM!

[FuShaoLei]

Great !

[csy99]

Thank you for the update. I update the file lib/plugins/filter/before_post_render/backtick_code_block.js according to b7e1150. However, the curly brackets in the code block still cannot be displayed correctly. Did I miss any changes?

[curbengh]

Make sure you have rebased to the latest hexojs/hexo master branch.