An array of the mentions found (including the leading @), in the order they appear.
Mentions
found in a block of text, symbol included.
A match only starts when the @ isn't immediately preceded by a
letter/digit/underscore, so an email address's @ (e.g.
user@example.com) is never mistaken for a mention.
Example
extractMentions('Thanks
Jordan
and @alex_dev for the review!');
// ['@jordan', '@alex_dev']
Extracts all