Annotate some java.net classes, mostly related to cookies.

[cpovirk]

Prompted by
google/xplat@18fd514.

[martinkretzschmar]

I have a new change for xplat/j2kt's HttpCookie

[cpovirk]

Thanks! I see that the Harmony tests you're using do explicitly check for handling of null cookie values, the case that I'm unsure about. I gather that the JDK lets them through, but it would be nice if it were explicit about that—or at least had some tests for it, but I haven't found any, nor have I found easily identifiable calls to new HttpCookie(name, null) in our codebase.

[martinkretzschmar]

Yes, the annotations were driven by that test. It passes when running with regular OpenJDK. But good question. Why should null be allowed as the cookie value.