Initial integration of differ to support iOS

[eyedol]

Fixes #383

[takahirom]

Looks great! Thank you for coordinating with other libraries and advancing our library foundation.
@eyedol, do you have anything to add to make this PR ready?

[eyedol]

Looks great! Thank you for coordinating with other libraries and advancing our library foundation.
@eyedol, do you have anything to add to make this PR ready?

I was going to look into how to use RoboCanvas to make an iOS implementation similar to how it's done with AwtRoboCanvas however, I couldn't figure out where to begin. Basically I wanted to work on the comments in RoborazziIos.kt

This is a temporary implementation for iOS.
We need to transition these implementations to Kotlin Multiplatform and RoboCanvas....

If you could point me in the right direction what you wanted to achieve with the comments in there, that would be great. Also if you think it will be a huge change in the end, we can tackle it with another PR. Let me know. Thanks.

[takahirom]

I think gradually moving the code to commonMain without using it for iOS will allow us to make progress without bugs, and then we can finally use it for iOS.

[takahirom]

Thank you for your contribution!