Introduce __stringnotstringable

[VincentLanglet]

Naming to debate ? __stringwithoutstringable ? __strictstring ?

intval($stringable) is never allowed, even without strict_types.

The current check in FunctionCallParameterCheck is

$this->ruleLevelHelper->accepts($parameterType, $argumentValueType, $scope->isDeclareStrictTypes());

either we're doing something like

$this->ruleLevelHelper->accepts(
      $parameterType,
      $argumentValueType,
      $scope->isDeclareStrictTypes() || in_array($functionName, ['floatval', 'intval', 'doubleval'], true)
);

either we have to introduce the opposite of StringAlwaysAcceptingObjectWithToStringType like I did.

Closes phpstan/phpstan#6560
Closes #1005

[ondrejmirtes]

Look at StringAlwaysAcceptingObjectWithToStringType. Every new Type implementation also has to override isSuperTypeOf to give correct answers.

You can test that in TypeCombinatorTest::testUnion and testIntersect.