[5.4] Allow boolean keys for Collection::groupBy method

[linaspasv]

The following PR adds support for boolean keys when used in groupBy method of \lluminate\Support\Collection. Related to #18672 issue.

[themsaid]

I think you can currently do:

$c = collect([
    ['yes' => true],
    ['yes' => false],
    ['yes' => false],
]);

$c->partition('yes');

This will partition the collection into two groups, trues and falses.

[linaspasv]

@themsaid it's not the case with an example you have provided. If you just took a look at an example I have provided in #18672 issue, where the is_pickup column in a model is being casted from an integer (value type in database) to boolean. At the moment, to make groupBy work, I need to remove boolean cast for that column in a model, as there is no way for groupBy to accept boolean keys. This somehow breaks an overall integrity between eloquent model and collections in this use-case.

p.s. in general PHP you are allowed to have true or false as an array keys, these convert to 1 and 0 accordingly.

I hope you got my point!