Return a literal string from route() when generating a URL

[bakerkretzmar]

This change would make using the route() function a little cleaner by removing the need to ever call .url(), bring its behaviour closer to matching Laravel's route() helper, and resolve a very annoying quirk with axios that required calling .url() to ensure that CSRF tokens are attached to the request.

When no arguments are passed to route(), it will continue to return a Router instance:

route(); // returns a Router
route().current(); // unchanged, returns a string (a route name)
route().current('home'); // unchanged, returns a boolean
route().params; // unchanged, returns an object
route().has('posts.show'); // unchanged, returns a boolean

However, now, if it's passed a name argument, it generates the URL and returns a string directly:

// before
route('home'); // returns a Router, which extends the String class, with a value of 'https://example.com'
route('home').url(); // returns 'https://example.com'

// after
route('home'); // returns 'https://example.com'

This PR also:

Removes the .with() method

This method was going to be deprecated in 1.0 since it isn't really necessary, parameters should always be passed as the second argument to route().

Removes the .withQuery() method

Query parameters can also be passed in the second argument to route(), mixed in with regular route parameters.

For edge cases like where a query parameter has exactly the same name as a route parameter, this PR adds a special _query parameter that will be added directly to the query string:

route('posts.show', {
    post: 4,
    _query: {
        post: 5,
    },
});
// 'https://example.com/posts/4?post=5'

Removes the .url() method

Calling .url() is no longer possible or necessary since route(...) with any arguments returns a string. To reduce repetition it was removed and its functionality was moved to the existing .toString() method on the Router class.

[jakebathman]

Looks good, I'm excited about this one 👍