fix isA*Of exception messages

[smoench]

No description provided.

[Nyholm]

Could you please rebase this PR?

[smoench]

PR is rebased

[smoench]

I also changed some error messages. You may have a look again?

[Nyholm]

I still feel that typeToString() is correct here.

I want to see string, AcmeService or boolean. I don't want to see the string value. Do I?

[smoench]

Well, I think it depends whether the value is passed as an object or string. WDYT about the following?

$isValueAString = \is_string($value);

if (!\is_a($value, $class, $isValueAString)) {
    static::reportInvalidArgument(sprintf(
        $message ?: 'Expected an instance of this class or to this class among its parents "%2$s". Got: %s',
        $isValueAString ? static::valueToString($value) : static::typeToString($value),  
        $class
    ));
}

An assertion about checking the type of value whether it is an object or string might be also a good idea

[smoench]

I updated the invalid test cases with passing an object and static::valueToString($value) is correct here.

[Nyholm]

Thank you for fixing this.