Allow knowledge of variadic callables

[philipobenito]

Considering the new Container::call functionality, I feel there should be a way to pass concrete runtime arguments to the callable separately to the dependencies that are defined.

It doesn't necessarily need to be >5.6 only, the callable would simply need to define the correct amount of arguments.

< PHP 5.6

$container->invokable('some_callable', function (SomeDependency $somedependency, $variadic1, $variadic2) {
    // ...
})->withArgument('SomeDependency');

$container->call('some_callable', ['variadic1 value', 'variadic2 value']);

>= PHP 5.6

$container->invokable('some_callable', function (SomeDependency $somedependency, ...$params) {
    // ...
})->withArgument('SomeDependency');

$container->call('some_callable', ['variadic1 value', 'variadic2 value']);

The main motivation behind this is to be able to use Container::call within a strategy for League\Route, allowing for dependencies to be defined per controller action but still pass in values from wildcard segments of the URI.

[philipobenito]

This currently works when reflecting on callable arguments, however is inconsistent when not using reflection, provide a more consistent solution that will work across the board.