This PR is a small refactor to align PR #68567 with the intentions of AiTutorContextHelper. A secondary nit that was addressed was to change UserAddedContext to UserAddedSelectionContext to further describe the additional context (code that the user "selects") that the user is adding.

Re: intentions of AiTutorContextHelper

The AiTutorContextHelper class is designed to be aware of a uniform set of context items that can be opted into by each lab / use-case. How the context item is formatted / added to the final context string is handled by getHiddenContextString, so the idea is that if something is only opted-into by a given lab that is fine, but if opted-in, it should be handled uniformly without having to provide any new lab-specific methods in the derived class.

The class is already pretty flexible in that it is a templated class and each use-case can provide its own internal data structure as a generic type parameter (T). Rather than defining a use-case specific getHiddenContextCallbackWebLab2, the additional context has been added to the WebLab2 specific type and its setAiTutorContext turns this specific context into a generic userSelection that is now an optional property of AiTutorContext and can be handled in the base class:

interface AiTutorWebLab2Params {
  source: MultiFileSource | undefined;
  longInstructions: string | undefined;
  selection: UserAddedSelectionContext;
}

I will cut the explanation short in the interest of time (the original PR is somewhat urgent), but if anyone has any questions or concerns, just let me know.

PR Creation Checklist:

• Tests provide adequate coverage
• Privacy impacts have been documented
• Security impacts have been documented
• Code is well-commented
• New features are translatable or updates will not break translations
• Relevant documentation has been added or updated
• User impact is well-understood and desirable
• Follow-up work items (including potential tech debt) are tracked and linked