fix: Correct decision notification payload type for getVariation feature test decision

[mjc1283]

Summary

In createProjectConfig, we attempt to create an object experimentFeatureMap whose keys are experiment IDs, and whose values are arrays of feature IDs. We loop over each experiment ID in each feature flag's experimentIds, and update experimentFeatureMap accordingly.

The problem occurs when one of these experiments is in a group (had a groupId property). The inner loop breaks out by returning false (this early iteration exit by returning false is a feature of lodash forEach). Then, any remaining experiment IDs are wrongfully excluded from experimentFeatureMap. For any of these skipped feature experiment IDs, the isFeatureExperiment function will wrongly return false, leading to an incorrect decision notification payload.

With this change, the loop always runs over all experiment IDs of each feature. The previous behavior of only assigning feature.groupId once is maintained.

Test plan

New unit tests for isFeatureExperiment function of project config module

Issues

https://optimizely.atlassian.net/browse/OASIS-5759

[mikeproeng37]

lgtm, can we run @Mat001 's FSC test on this branch and confirm that it passes?

[coveralls]

Coverage increased (+0.005%) to 97.511% when pulling 8929d58 on mcarroll/OASIS-5759 into 9a4d96b on master.