Function maskChineseMobile

maskChineseMobile(text?: string | null): string | undefined
Returns a masked Chinese mobile phone number, which keeps the first 3 and last 4 characters

The +86 or 86 country code prefix is kept as-is if present in the given text
Parameters
- Optionaltext: string | null
  The text to mask
Returns string | undefined
a masked Chinese mobile phone number, or undefined if the given text is invalid
Author
David Hsing
Example
```
maskChineseMobile(undefined);    // undefined
maskChineseMobile('13812345678');    // '138****5678'
maskChineseMobile('+8613812345678');    // '+86138****5678'
maskChineseMobile('+86-13812345678');    // '+86-138****5678'
maskChineseMobile('8613812345678');    // '86138****5678'
maskChineseMobile('12345678901');    // undefined
```