Add the trailing_comma_single_line option to function_declaration

[paulbalandan]

Description

$ vendor/bin/php-cs-fixer describe function_declaration
Description of function_declaration rule.
Spaces should be properly placed in a function declaration.

Fixer is configurable using following options:
* closure_function_spacing ('none', 'one'): spacing to use before open parenthesis for closures; defaults to 'one'
* trailing_comma_single_line (bool): whether trailing commas are allowed in single line signatures; defaults to false

...

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide