Change dump pair to using associative array

Example
```php
// before
DumpfPair::dump('label_for_var_x', $x, 'label_for_var_y', $y);

// after
DumpfPair::dump([
    'label_for_var_x' => $x,
    'label_for_var_y' => $y,
]);
```

Consider support also multiple arrays as arguments, e.g.:
```php
DumpPair::dump(
    ['label_for_var_x' => $x],
    ['label_for_var_y' => $y],
);
```