Deprecate NamingConventions::isEqual()

[jrfnl]

From a couple of previous discussions had over the last year or so, it looks like strtolower() will not affect non-ASCII chars, so a comparison between two names, which have both been lowercased, should actually result in a PHP name handling compliant comparison.

Would be good to double-check this with some extra tests with more non-ASCII names, but if the above turns out to be true in all cases, I believe the method should be deprecated and can then be removed in the next major of Utils after this has been double-checked.

Refs:

• https://www.php.net/manual/en/function.strtolower.php
• https://3v4l.org/AQ93s