Implement NegotiateAuthentication API (#70720)

Implement NegotiateAuthentication API (#70720)

* WIP: Add implementation of NegotiateAuthentication

Switch System.Net.Http to use NegotiateAuthentication
Fix IsCompleted in managed NTLM implementation

* WIP: Update error code mapping

* Spanify input of GetOutgoingBlob

* Update comments

* Move NegotiateStreamPal.Encrypt/Decrypt to shared sources. Unix implementation already had them and they get trimmed anyway.

* Revert accidental change

* Build fixes.

* Fix error handling condition

* Update error mapping based on HttpListener usage.

* WIP: HttpListener test

* Move workaround from HttpListener to low-level SSPI code

* Fix build

* Clean up

* Revert "WIP: HttpListener test"

This reverts commit 18d7d93f04c93e048efcaca0f3c55c3f1f73516a.

* Convert System.Net.Http.FunctionalTests to use NegotiateAuthentication instead of NTAuthentication

* Dispose the identity along NegotiateAuthentication

* Modify unit tests to use the new API

* Add exceptions for invalid inputs/states

* Remove tvOS unsupported marker, managed NTLM is used on tvOS

* Apply suggestions from code review

Co-authored-by: Stephen Toub <stoub@microsoft.com>
* Fix typo

* Remove reference equality checks from IsNTLM/IsKerberos

* Remove NTAuthentication.AssociatedName to make it more obvious which exceptions are thrown

* Add comment

* Add more tests, handle unsupported protocols

* Handle NotSupportedException from NTAuthentication constructor

* Add workaround for linker issue

* Apply suggestions from code review

Co-authored-by: Stephen Toub <stoub@microsoft.com>