View source for XMB Code Standards

Work toward adopting [https://www.php-fig.org/psr/psr-12/ PSR-12] began in 2024.  New XMB code contributions should conform to that document.  Here are some of the highlights:
* Line endings are Unix-style LF.
* File endings are a single LF after the last non-blank line.
* No trailing whitespace.
* No space after an opening parenthesis.
* No space before a closing parenthesis.
* Indents consist of 4 spaces.