Add support for the Partitioned cookie attribute

[amcasey]

...to support CHIPS (Cookies Having Independent Partitioned State).

Fixes #53224
Fixes #55370

[halter73]

@blowdart I just left a comment on the issue you filed for this, but I'll repeat it here. Are we really doing this for an expired draft spec that's only supported by chromium-based browsers when the workaround is nearly as easy to use as the proposed API?

New API:

options.Cookie.Partitioned = true;

Workaround:

options.Cookie.Extensions.Add("partitioned");

We did approve the API, but we were a little rushed. And I don't think the workaround was ever demonstrated. The simplicity of the workaround really makes me want to hold off on this until the spec is final.

[blowdart]

I take your point about the spec, but it's one of those that is unlikely to change (in my opinion) now that cookie has full throttle committed to it.

[amcasey]

I take your point about the spec, but it's one of those that is unlikely to change (in my opinion) now that cookie has full throttle committed to it.

I'm guessing that was meant to be "chrome has full throttle committed to it".

[blowdart]

Mozilla views it positively
Webkit views it positively

(Basically we'll add it soon)

Google started the staged rollout in chrome for 1% of users. although they stopped because regulators objected.

[amcasey]

@blowdart @halter73 Would it be preferable to merge early and get feedback but be ready to pull it or save this until the last minute to build confidence that browsers will actually adopt it?

[gfoidl]

I don't know if it matters here, as the enum isn't embedded in a type.

Suggested change

	private enum MessagesToLog
	private enum MessagesToLog : byte

to make the enum smaller (1 byte vs. 4 bytes for int (default)).

[amcasey]

Thanks! I considered that, but decided against it for two reasons. First, I'm expecting there to be more flags in the future. I've already added one since the PR began. 😆 Second, I figured space saving was probably less valuable than simplified alignment on the stack (though I didn't measure).

[dotnet-policy-service]

Looks like this PR hasn't been active for some time and the codebase could have been changed in the meantime.
To make sure no conflicting changes have occurred, please rerun validation before merging. You can do this by leaving an /azp run comment here (requires commit rights), or by simply closing and reopening.