New sniff: change long list syntax to short list syntax

[jrfnl]

Sniff basics	-
Fixable for PHP:	7.1+
Sniff type:	Modernize
Fixer type:	Safe

Short description

PHP 7.1 introduced a short list syntax.

Related PHPCompatibility sniff(s):

• ShortList (open PR PHP 7.1: New sniff to detect short list syntax for symmetric array destructuring PHPCompatibility#654)

PHP manual references:

• The shorthand array syntax ([]) may now be used to destructure arrays for assignments (including within foreach), as an alternative to the existing list() syntax, which is still supported.

  http://php.net/manual/en/migration71.new-features.php#migration71.new-features.symmetric-array-destructuring

• https://wiki.php.net/rfc/short_list_syntax

Example code:

Detect the following code pattern(s):

list($id1, $name1) = $data[0];

foreach ($data as list($id, $name)) {
    // logic here with $id and $name
}

And fix these to:

[$id1, $name1] = $data[0];

foreach ($data as [$id, $name]) {
    // logic here with $id and $name
}