Adding fn/cva helper function

[rojtjo]

In simple projects my definitions often just live in my view files and it always bugged me to type the FQCN when using cva.
These changes add the fn\cva helper which accepts the same parameters as the FeatureNinja\Cva\ClassVarianceAuthority::new method.

$button = fn\cva(
    ['font-semibold', 'border', 'rounded'],
    [
        'variants' => [
            'intent' => [
                'primary' => ['bg-blue-500', 'text-white', 'border-transparent', 'hover:bg-blue-600'],
                'secondary' => 'bg-white text-gray-800 border-gray-400 hover:bg-gray-100',
            ],
            'size' => [
                'small' => ['text-sm', 'py-1', 'px-2'],
                'medium' => 'text-base py-2 px-4',
            ],
        ],
        'compoundVariants' => [
            [
                'intent' => 'primary',
                'size' => 'medium',
                'class' => 'uppercase',
            ],
        ],
        'defaultVariants' => [
            'intent' => 'primary',
            'size' => 'medium',
        ],
    ],
);