Support truthy-string/non-falsy-string pseudo-type #302
Description
PHPStan and Psalm both support a pseudo-type called truthy-string (with alias non-falsy-string), which represents a string that is not '' and not '0'... in other words, a string that will always be true when cast to bool. (Another way it can be thought of is as a subset of non-empty-string that excludes 0.)
The PHP Tools extension does not currently support this pseudo-type, and treats it like a class.
