Bug report

I tried a PR to fix it (phpstan/phpstan-src#3400) but currently I'm stuck with the fix and dunno if it doesn't imply biggest changes about how PHPStan deals with list... so I prefer to discuss about this issue with you @ondrejmirtes first.

It may be surprising but the code

$a = [1, 2, 3];
unset($a[2]);

var_dump(array_is_list($a));

display TRUE. See https://3v4l.org/XX2fU

The php method only checks the array key, and not the next array key.
Which also means unsetting a value to a non-list might give a list. (cf example)

So I'm not sure

• If we have to "recompute" the isList property when unsetting a value (and how ?)
• If the isList method should become dynamic instead of relying on a static property, with an implementation like:

			$this->isList = TrinaryLogic::createYes();

			foreach ($this->keyTypes as $i => $keyType) {
				$this->isList->and((new ConstantIntegerType($i))->isSuperTypeOf($keyType));
			}

			$optionalKeyNumber = count($this->optionalKeys);
			if (
				($optionalKeyNumber > 1)
				|| ($optionalKeyNumber === 1 && !$this->isOptionalKey(count($this->keyTypes) - 1))
			) {
				$this->isList->and(TrinaryLogic::createMaybe());
			}

• If we should just ignore the case a non-list become a list, and fix the case where we unset the last element
• If we should just ignore both case and close the issue (?)

Code snippet that reproduces the problem

https://phpstan.org/r/7b40683e-010c-4d5a-96dc-9fda4ce27797

Expected output

First call will always evaluate to true.
Second call will always evaluate to false.
Third call will always evaluate to true.

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