Run tidy

This should fix most of the remaining issues with tabs and spaces
being mixed in tests.

Change Attribute Syntax from @@ to #[]

Implement Shorter Attribute Syntax

RFC: https://wiki.php.net/rfc/shorter_attribute_syntax

Closes GH-5796.

Co-authored-by: Martin Schröder <m.schroeder2007@gmail.com>

Consistent file naming.