New sniff: change casts to (unset)

[jrfnl]

Sniff basics	-
Fixable for PHP:	All
Sniff type:	Modernize
Fixer type:	Risky

Short description

PHP 5.0 introduced an (unset) type cast for feature completeness. This type cast has been deprecated as of PHP 7.2 and is slated to be removed in PHP 8.0.

Related PHPCompatibility sniff(s):

• NewTypeCasts
• DeprecatedTypeCasts

PHP manual references:

• http://php.net/manual/en/language.types.type-juggling.php#language.types.typecasting

Example code:

Detect the following code pattern(s):

$a = (unset) $b;
$b = (unset) $b;

And fix these to:

$a = null;
unset( $b );

Notes for implementation of the sniff:

• Type casts only have effect when the result is assigned to something. Type casts are not done by reference!