[8.x] Add undot() method to Arr helpers and Collections

[amiranagram]

This PR adds support for elevate method in array helpers and collections.

This method basically does the opposite of Arr::dot(), it takes an associative array and converts it to a multi-dimensional one based on keys with dot notation.

For example if we take this array and pass it through Arr::dot():

$original = [
    'user' => [
        'name' => 'foo',
        'occupation' => 'bar',
    ]
];

$dotted = Arr::dot($original);

We would get a flattened associative array:

$dotted = [
    'user.name' => 'foo',
    'user.occupation' => 'bar',
];

Now if we elevate the dotted array we should get the original.

$elevated = Arr::elevate($dotted);

$elevated ≡ $original

Same goes for collections and lazy collections. Not sure if "elevate" is the best name for it, so I'm open to suggestions.

Cheers.

P.S. Will take a look on how to test if a collection is actually lazy and add an additional test. Some help is welcome, of course.

[johanrosenson]

This has been suggested before as undot, which i personally think is a great name, pretty self explanatory.

#38167
#33845
#13897
#4735
#4292

sadly undot have not been merged so far.

[amiranagram]

@johanrosenson Welp, wasn't aware that this was suggested before.

Agree, undot sounds way better. Elevate is an antonym of flatten as far as I know and flatten is something else entirely.

[taylorotwell]

Since this keeps coming back up as a PR I will go ahead and include it.