Update array_filter signature in PHP 8.0 to allow null as callback

[andyexeter]

The callback parameter of array_filter has been nullable since PHP 8.0 but PHPStan doesn't currently allow it:

https://phpstan.org/r/307000c9-843b-42af-9910-baa02ec72f2f

[andyexeter]

I'm not sure why the tests are failing. All I did was copy the signature from the main functionMap.php file and add |null to the callback signature.

[ondrejmirtes]

Please reproduce your problem in CallToFunctionParametersRuleTest. You'll find that it will still most likely fail.

array_filter is a special function. You need to add NullType here too:

phpstan-src/src/Reflection/ParametersAcceptorSelector.php

Lines 174 to 180 in d846b02

	new CallableType(
	$arrayFilterParameters ?? [
	new DummyParameter('item', $scope->getIterableValueType($scope->getType($args[0]->value)), false, PassedByReference::createNo(), false, null),
	],
	new MixedType(),
	false,
	),

(create new UnionType of that CallableType and new NullType).

Please disregard the irrelevant failures.

[andyexeter]

@ondrejmirtes I think this is ready for review, the failing tests appear unrelated.

[ondrejmirtes]

Thank you!