[NOTE] [Examples] Use Prettier to Auto-format our Examples Code and Change to Two Spaces Indent

[Yi Shen <sh...@gmail.com>]

Dear community,

Recently we are rewriting our examples with TypeScript[1] so the example
page can provide a better intelligent experience to developers. These TS
examples can also help us testing our exported DTS files.

During this rewriting, I found our examples have lots of code style issues.
So I'm going to auto-format our examples codes with prettier.
The result of the formatted example code will be the more near to the
commonly used JS style guide in the community. The biggest change will be
changing the indent from 4 spaces to 2 spaces.
There are two major pros about this change:
1. Code can be tighter. Which is very useful when it's being displayed in a
very limited space on our example page[2]
2. Developers can do less formatting work when they use our example code.

These changes will only be applied to the example code. It won't affect our
source code. Let us know your thoughts before we publishing it online.
Thanks a lot!

[1]
https://github.com/apache/echarts-examples/tree/gh-pages/public/examples/ts
[2] https://echarts.apache.org/examples/zh/editor.html?c=confidence-band

-- 
Yi Shen
Apache ECharts PMC