JQL with a sprint clause does not return Next-gen subtasks

Issue Summary

Change to be made in Search to account for Next-gen subtask to parent relationship as it currently only looks at the classic relationship.

Steps to Reproduce

Create a sprint
Add an issue to the sprint
Add subtasks to the issue
Go to GIN
Search based on the JQL "sprint = <Your sprint>"

Expected Results

The result set includes your issue as well as the subtasks.

Actual Results

Subtasks are not included in the result

Workaround

Currently there is no known workaround for this behavior. A workaround will be added here when available.