Check what type of 'use' statement a token is part of.

The T_USE token has multiple different uses:

1. In a closure: function () use ( $var ) {}
2. In a class, to import a trait: use Trait_Name
3. In a namespace, to import a class: use Some\Class;

This function will check the token and return 'closure', 'trait', or 'class',
based on which of these uses the use is being used for.

@since 0.7.0

@param int $stackPtr The position of the token to check.

@return string The type of use.