Reimport for a single FBX with multiple meshes will add all mesh pieces instead of the single mesh.

When using a single FBX with multiple meshes that is imported as individual meshes, if you reimport after updating only a single mesh or a few of them the entirety of FBX will be imported and added to this single imported mesh.

This is a regression of behavior from 4.13 that is now broken in 4.14 and 4.15.

Working: 4.13 Binary CL-3172292
Broken: 4.14 Binary CL-3195953
Broken: 4.15 Dev-Rendering CL-3201999

1. Import any FBX asset with multiple meshes
2. In the Import options uncheck "Combine Meshes"
3. Change one of meshes in a modeling program.
4. In the content browser select only the mesh that was changed and right-click > Reimport

Regression: Yes

Results: When using reimport for a single mesh that was imported with an FBX that contained multiple meshes all the meshes will be imported to this single mesh.

[4.14 P3] FBX Reimport Static Mesh combines all the mesh