Stale references in asset panel context menu

[marklundin]

The "References" context menu in the asset panel can become stale, showing a list of inaccurate references.

Steps to repro

1. Create a "New Material" in the Asset Panel
2. Create a new Box Primitive (New Entity > 3D Entity > Box)
3. Assign the "New Material" to the Box Materials
4. Create a second Box Primitive (New Entity > 3D Entity > Box)
5. Assign the "New Material" to the second box
6. Right click on the "New Material > References" - Note 2 references listed
7. Remove the material on one of the box primitives
8. Right click on the "New Material > References" - Still 2 references listed

Refreshing the project updates to display the correct references

Likely related to #1473.

[SaadHaider7]

This has been happening for a long time and has resulted in many hours of frustration due to deleting assets which were referenced in the scene but the reference menu not showing any references.