Update SIPHeaderList to inherit SequencedCollection added in OpenJDK 21

java.util.List now extends SequencedCollection interface. java language
doesn't allow overloading a super-interface's method with
an incompatible return type.

In order to expose SequencedCollection API in the build time,
SIPHeaderList needs to be updated to return a compatible return type.

Bug: 320460092
Test: m droid
Change-Id: Iea134996c36b670964c614a01e1f2cb26a76082e