[8.x] Allow request input to be retrieved as a collection

[erikgall]

Description

This PR adds the ability to retrieve input from an incoming request as a collection. In our codebase, I have noticed that we are commonly retrieving input from the request, defaulting it to an empty array and passing it to the collect helper. If a key is not given it will return all of the request's input as a collection. If a key is not found, it will default the input to [] and return an empty collection.

Before

collect($request->input('users', []))->each(function ($user) {
    // ...
});

After

If approved, it would allow for a straight forward shortcut to retrieve the requested input / input key as a collection:

$request->collect('users')->each(function ($user) {
    // ...
});

Thanks!