Fix `PaginatedResult` and `HttpPaginatedResponse` not follow the spec

[VeskeR]

See discussions in #2021.
HttpPaginatedResponse does not implement HP2 and fails when those methods are called.
PaginatedResult has a vague spec definition and inconsistent implementation across SDKs. TG2 suggests paging headers may not be returned by the REST API, so the spec for pagination methods like #first and #next should cover the expected behavior in such a case. Currently it only covers the behavior for #next when paging header is missing TG4.

┆Issue is synchronized with this Jira Task by Unito