Mainland Phone Number without Area Code

Closes #906

Upstream MR

What does this MR do and why?

Users can sign in with mainland phone numbers without area code +86.

• allow users to sign in without input area code for mainland phones
• update input label for phone on sign in page

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. register a new user with mainland phone number
2. goto sign in page
3. fill login field with your phone number WITHOUT area code
4. you should sign in successfully

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.