Allow a cookie without a domain to be set on Android

[bagedevimo]

The other CookieManager implementations in Flutter allow for no domain,
as the Android CookieManager implementation. By providing a default
domain, applications cannot opt-out of the default
CookieManager.setCookie behaviour (which prepends a "period" to the
domain), which is treated as a different domain by Webkit on Android.
This leads to multiple cookies for the same URL if the server serves a
cookie without a domain, or with a domain that does not contain a
leading period.

Note, iOS's setCookie doesn't take a url parameter (at least in the way
it's called from flutter_inappwebview) and instead this is passed an
attribute on the HTTPCookie object itself (originURL). When constructing
a HTTPCookie you must supply either originURL OR domain. Both a
permitted, but at least one must be present. [1]

By making domain optional, without a default, on both platforms,
consumers can now set cookies that don't use the domain attribute but
still allows for setting a domain when required.

[1] https://developer.apple.com/documentation/foundation/httpcookie/1392975-init

Testing and Review Notes

Existing usages shouldn't be affected, unless they were relying on this default behavior which kinda wasn't documented so I dunno how much we care about that contract?

Screenshots or Videos

N/A

To Do

• double check the original issue to confirm it is fully satisfied
• add testing notes and screenshots in PR description to help guide reviewers
• request the "UX" team perform a design review (if/when applicable)

[pichillilorenzo]

Thanks! @all-contributors please add @bagedevimo for code

[allcontributors]

@pichillilorenzo

I've put up a pull request to add @bagedevimo! 🎉