Introduce Yoda Conditions Sniff and Unit Tests

I spent ages trying to figure that out yesterday and failed which is why it's split into 3.

To account for shorter comparisons like '==' and '!=' it may need to be:
<code>preg_match_all( '#([!=][!=]=? \b(true|false|[\'"0-9])\b)#si', $string, $matches );</code>