[5.8] Make register method in the ServiceProvider as part of the co…

…ntract

 In the laravel/framework#27067 pr was added DeferrableProvider service provider.
 This Pr will add pretty the same thing.
 In case, if it will be accepted then I will add documentation for this.

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Also i thing will be good to add diferent contract for the:
- method `boot`
- property `singletons` and `bindings`

ViewServiceProvider.php

@@ -8,8 +8,9 @@
 use Illuminate\View\Engines\CompilerEngine;
 use Illuminate\View\Engines\EngineResolver;
 use Illuminate\View\Compilers\BladeCompiler;
+use Illuminate\Contracts\Support\RegistrableProvider;
 
-class ViewServiceProvider extends ServiceProvider
+class ViewServiceProvider extends ServiceProvider implements RegistrableProvider
 {
     /**
      * Register the service provider.