[5.6] Add missing functions in Dispatcher contract

[Naouak]

see #22951

[carusogabriel]

This has introduced an error ⚠️

PHP Fatal error:  Class Illuminate\Support\Testing\Fakes\BusFake contains 3 abstract methods and must therefore be declared abstract or implement the remaining methods (Illuminate\Contracts\Bus\Dispatcher::hasCommandHandler, Illuminate\Contracts\Bus\Dispatcher::getCommandHandler, Illuminate\Contracts\Bus\Dispatcher::map) in /var/www/framework/src/Illuminate/Support/Testing/Fakes/BusFake.php on line 8

[Naouak]

@carusogabriel Can you point out which test is giving the error? I have a commit ready fixing it but I want to check it is correctly fixing it.