Refactor spec helper stub_session

What does this MR do and why?

In !148548 (merged), the stub_session spec helper was updated to allow a new user_id param. To avoid lots of unnecessary updates in that MR, we left a less than ideal method signature. This is a follow-up refactor to reduce ambiguity and update all usage to ensure session data is passed as a hash via a keyword arg.

!148548 (merged) must be merged prior to this MR.

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