New mutator proposal: remove item from literal array

[MidnightDesign]

TL;DR: A "remove item from literal array" mutator would be great.

Is your feature request related to a problem? Please describe.
I'm doing kind of a fingerprinting/checksum thing, like:

$relevantData = [$item->foo(), $item->bar()];
$fingerprint = md5(json_encode($data));

I just added a third item to the list of relevant data: [$item->foo(), $item->bar(), $item->baz()]. A little later I realized that whenever the output of baz() changes, the output of foo() changes too. So I could remove the first item and have the (functionally) same thing.

Infection didn't check if the array item was required.

Describe the solution you'd like
Infection should warn me that an element in an array literal could be removed with the tests still passing.

[localheinz]

I think it is good idea - I believe the challenge here is to decide how many mutations we want to yield from such a mutator.

[maks-rafalko]

Since we are trying to keep balance between the number of generated mutants and the speed of infection, I would say that generating N mutations for an array with N elements is too much.

What about generating 1 mutation by default (e.g. removing the first element) and have a setting to enable N mutations if someone needs a hardcore mode? :)

{
    "mutators": {
        "RemoveArrayItem": {
             "settings": {
                 "remove": "first" (first|last|all)
             }
        }
    }
}

[MidnightDesign]

Maybe something like "N mutations for an array with N elements, up to X elements. If there are more than X elements, generate only one mutation for the first element". (Where X could be configured.)

[localheinz]

Perhaps something like using a --level option, similar to phpstan/phpstan?

Then it wouldn't be necessary to have a complicated configuration, but something that applies to all mutators that could potentially yield more than one mutation?

Also see #636.