[6.x] Add implodeForHumans method to the string helpers class (Str).

[amestsantim]

This PR adds an implodeForHumans method to the string helper, Str, class.

The method can be a drop-in replacement for implode() and will act the same way if the last parameter is not passed, which means it can easily be swapped in and out without breaking your code.

It follows the "Oxford comma" way of treating the coordinating conjunction (usually 'and' or 'or'). This method can be very useful when trying to make human-readable error messages from an array of words or sentences.

Examples:

Str::implodeForHumans(', ', ['cats'], ' and ');
// cats

Str::implodeForHumans(', ', ['cats', 'dogs'], ' and ');
// cats and dogs

Str::implodeForHumans(', ', ['cats', 'dogs', 'cows'], ' and ');
// cats, dogs, and cows

Str::implodeForHumans(', ', ['cats', 'dogs']);
// cats, dogs

The PR includes a test method (testImplodeForHumans) that tests most of the possible cases.

[bonzai]

#27723

https://laravel.com/docs/5.8/collections#method-join

[amestsantim]

Oh, didn't know that the collection's join method could take a second argument...
Though it does not discriminate when there are only two elements in the collection... that might be reason enough to keep this one or not!
Thanks anyway!

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

If you feel absolutely certain that this code corrects a bug in the framework, please "@" mention me in a follow-up comment with further explanation so that GitHub will send me a notification of your response.