[UnusedVariable] Add setting to ignore destructuring

[wdoug]

I know that PHP supports skipping elements when destructuring from an array:

$array = [1, 2, 3];
[, , $c] = $array;

However, I often find it nice to have named variables for destructuring even if they aren't all used.

Can we add a new setting for that rule similar to ignoreUnusedValuesWhenOnlyKeysAreUsedInForeach that allows ignoring unused variables in destructuring?