[BUG] Assignee filter should consider only the values present in the Reassign modal

• Type: Technical Task
• Status: Closed
• Priority: Minor
• Resolution: Completed
• Affects Version/s: None
• Fix Version/s: Master
• Component/s: Workflow
• Labels: None
• Git Pull Request: https://github.com/brianchandotcom/liferay-portal/pull/86378

Current issue: Assignee filter should consider only the values present in the Reassign modal

Steps to reproduce:

1. Associate Single approver with blogs entry
2. Create 10 new users (user1, user2, user3, ..., user10)
3. Create 10 blog entries and assign each entry to a different user
4. Go to CP > Metrics > Single Approver > Click on the Pending Items number
5. Select the entries assigned to user1 and user2 and open the bulk reassign modal
6. Open the Assignee filter

Actual result: All assignees are available to be filtered, even when there is no task assigned to some users

Expected result: Only users assigned to the tasks that are going to be reassigned should be available to be filtered

Environment:
master DXP: c9a9b9f196b1f1dd5cf83cddf6bf1f1f8c9ff814
Updated on: Wed Feb 12 16:51:12 2020 -0800