Use Macroable or allow adding custom attributes to RouteRegistrar

[bilogic]

laravel/ideas#741

If we add a new mixin/macro on Illuminate\Routing\Route, it cannot be accessed from RouteRegistrar because the $allowedAttributes are hardcoded.

Since Route is macroable, it would be great if those macros can also be accessed from RouteRegistrar.

I found a need for this when trying to define an icon for each route, which can be turned into a menu/breadcrumbs.

[marinario]

@bilogic any work around for this?

[henzeb]

Closures. Can be bound to any object, anywhere anytime, and from there you can access the properties from RouteRegistrar. Just be sure you bind to the object and then use the context (actual class) the variable is in.