Refactor counts logic for work item lists

What does this MR do and why?

Updates the logic around fetching work item counts:

1. When using consolidated list, counts for tabs are no longer fetched
2. Uses a different query to figure out whether or not to display the 'you have no items' message (hopefully a little quicker)

References

Screenshots or screen recordings

Before	After

How to set up and validate locally

Toggle work_item_planning_view and check the /work_items, /issues, and /epics pages when available. It's should load with no errors, empty projects or groups should show the 'you have no issues/epics/etc' messages.

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Relates to #578203