Adding initial annotations for UnityEngine and UnityEditor not null items

[bigbadtrumpet]

I added the items that I know for certainty are not null. Probably could be more added in the future but this gets the most common items that can never be null.

[citizenmatt]

Looks great, thanks! I'll review properly on Monday - I need to catch up with a number of issues and PRs.

Thanks for submitting!

[citizenmatt]

Not sure this is accurate. The XML docs for Component.transform state:

The Transform attached to this GameObject (null if there is none attached).

[citizenmatt]

Thanks for the pull request! I need the annotations to address other issues, so I'm merging the PR as it stands, but I'm not sure about the NotNull attributes that I've commented on above, if you could take a look, please? If you let me know, I can easily edit the two lines.

Thanks!

[bigbadtrumpet]

Yea I have posted a question on Unity's forums to ensure that my assumptions are correct. However it is my understanding (despite the confusing documentation) that the things are marked are correct. As soon as I get any information to the contrary I will update it with a new pull request!

[citizenmatt]

Awesome, thanks. I think I'll comment them out for now, as it goes against the docs. Would be great to get clarification, though.