Allow to call isInstanceOf and equivalent assertions on nullable types

[jcornaz]

Description

It seemed odd to me that fun Any?.shouldBeInstanceOf(className: KClass<*>) was accepting nullable receiver but fun <reified T : Any> Any.shouldBeInstanceOf(): T not.

This PR make possible to call the following functions on a nullable type:

• shouldBeInstanceOf
• shouldNotBeInstanceOf
• should be instance of
• should not be instance of
• shouldHaveTheSameClassAs
• shouldNotHaveTheSameClassAs

I added tests to assert the expected behavior when called on a null reference.

Checklist

• I've added my name to the AUTHORS file, if it wasn't already present.

[MarkusAmshove]

Oh didn't catch that when implementing, thanks for the PR 👍

[MarkusAmshove]

This is part of the just released v1.44