Emoji renders as question marks with MySQL "utf8" encoding

Summary:
On an XWiki installation that uses MySQL, emoji characters render as question marks.

Steps to Reproduce:

• Setup XWiki with MySQL as the database
• Create a wiki page with some emoji characters
• View the page

Expected Result:
The emoji should render correctly

Actual Result:
The emoji characters renders as question marks.

Is this a Regression?
No, this is not a regression and appears to be an underlying issue with XWiki + MySQL

Notes:

• This is caused by MySQL's default encoding (in XWiki) which is "utf8" and not "utf8mb4" (4-byte UTF to store the full unicode character set).
• Changing XWiki's default data encoding for MySQL to be "utf8mb4" should fix the issue.