[11.x] adds formatKeysWith method to Arr

[smetzdev]

Hey folks,

this PR adds makes it possible to format the key names of an associative Array with any given callable.

  $formatedArray = Arr::formatKeysWith(["hello_laravel" => true ], [Str::class, 'camel']); 
  // ["helloLaravel" => true ];

I've also added a third $depth parameter, which defaults to the maximum integer

Greetings from Germany,
Sascha

[taylorotwell]

Thanks for your pull request to Laravel!

Unfortunately, I'm going to delay merging this code for now. To preserve our ability to adequately maintain the framework, we need to be very careful regarding the amount of code we include.

If applicable, please consider releasing your code as a package so that the community can still take advantage of your contributions!

[taylorotwell]

You can use mapWithKeys