[12.x] feat: add PolicedBy attribute and policy caching

[calebdw]

Hello!

This adds a new PolicedBy attribute to easily associate a policy with a model (can change the name if there's better ideas):

#[PolicedBy(PostPolicy::class)]
class Post extends Model
{
}

To improve performance and avoid having to re-guess policies on every request (they should not be changing in production) I also added a new artisan policy:cache command that also executed as part of artisan optimize (same for the *:clear variants)

Note, I added a new method, Gate::getPolicyClassFor(), so I could get the policy class without incurring a performance penalty of newing up the instances just to get the class from the instance.

Finally, I added a ->withPolicies method to the ApplicationBuilder so that users can pass other directories like:

// bootstrap/app.php
return Application::configure(basePath: dirname(__DIR__))
    ->withPolicies(new LazyCollection(
        fn () => Finder::create()
            ->directories()
            ->in([app_path(), base_path('modules')])
            ->path('Models')
    )->keys())
    // ...

Thanks!

[taylorotwell]

I might call it something like UsePolicy to match UseFactory.

[taylorotwell]

I don't really love the amount of code added plus a new cache command just to unlock attribute customization of policies. Policies can already be auto-discovered (even outside of app directory style applications) by just following a pretty basic convention.

[calebdw]

@taylorotwell, I combined two ideas into one when I should have split them out