[10.x] Register policies automatically to the gate

[ahmett]

This PR aims to enhance eventual consistency between parts of the framework.

Unlike the other features of the framework (observers, listeners, etc.), policies don't get automatically registered while AuthServiceProvider is booting. It is required to call the registerPolicies method.

And I think this is redundant.

Logic preserves its natural behavior. It doesn't affect auto-discovery, defined with the Gate::guessPolicyNamesUsing method.

I also create a PR in the skeleton repo to remove redundant calling of the registerPolicies method.

[ahmett]

Docs updated according to this PR, see: laravel/docs#8584
Skeleton repo also updated, see: laravel/laravel#6108

[taylorotwell]

Won't they be registered twice if we make this change and people don't update their skeleton?

[ahmett]

@taylorotwell It won't because we are replacing that method. Existing codebases with 10.x only need to delete that method call from the service provider. I already documented this in upgrade docs.

Edit: We also could re-add the registerPolicies method with an empty body to preserve compatibility with 10.x codebases whose doesn't delete that method call. This makes deleting the method call optional.

Example:

/**
  * It's unused and does nothing, if you are calling this method you can safely delete the method call.
  *
  * @deprecated Will be removed in a future Laravel version.
  */
public function registerPolicies(): void {}