[FSSDK-11823] make Activate listener payload type backwards compatible

[raju-opti]

Summary

The current type of activate listener payload is not backwards compatible with the type in v6.0.0. This PR makes it compatible.

Test plan

Issues

• FSSDK-11823

[coveralls]

coverage: 79.144% (+0.001%) from 79.143%
when pulling 6735577 on raju/holdout-noti
into fb5e012 on master.

[Copilot]

Pull Request Overview

This PR makes the activate listener payload type backwards compatible with v6.0.0 by separating experiment and holdout fields instead of using a union type.

• Separates the experiment field into distinct experiment and holdout fields in ActivateListenerPayload
• Adds runtime type checking with isHoldout function to properly populate the correct field
• Updates notification handling to conditionally set either experiment or holdout based on the decision object type

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
lib/shared_types.ts	Adds isHoldout type guard function to distinguish between experiments and holdouts
lib/optimizely/index.ts	Updates activate notification logic to separate experiment and holdout into distinct fields
lib/optimizely/index.tests.js	Updates test expectations to include the new holdout: null field
lib/optimizely/index.spec.ts	Updates test spy names and adds validation for the new activate notification payload structure
lib/notification_center/type.ts	Modifies ActivateListenerPayload type to have separate experiment and holdout fields
lib/feature_toggle.ts	Updates holdout feature toggle and adds conditional type helper

Comments suppressed due to low confidence (1)

lib/feature_toggle.ts:1

• Import statement references holdout and IfActive from a file that is being modified in this PR. The IfActive type is newly added but holdout is a function, not a type. This import may cause issues if the function is being used as a type in the import context.

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