I noted a new popover in mesh edit mode:
I try to play with it, add custom split normals, auto smooth, but see nothing happens with model.
How to use it, or it just doesn't work?
It seems normals can be set with tools like Set From Faces, Average Normals, Point Normals to Target or Smoothen, but Set Strength or Face Select in the Mesh->Normals menu does not work at all unless Weighted Normal Modifier is added and Face Influence in it is enabled. Those Face Strength settings are the same as in Properties Editor's Active Tool and Workspace tab and they are for Set Strength in Mesh->Normals menu:
Keeping in mind how absolutely ridiculous and unnecessarily complex this functionality is, I would be surprised if it makes it into 2.80 release as it is now. Hopefully it will change to something a lot more logical.
I believe this panel is used for some operations on normals (some description in "Custom Normal Tools and Modifier" section): Mesh -> Normals.
Normal Vector should be used for operations under "Normal Vector" section (thought I think Copy and Paste don't use it and reset UI option to (0,0,1) or even use this vector for Copy/Paste). Add and Multiply seem to work.
Face Strength is used for 2 operations in "Face Strength" section: Face Select and Set Strength to be used with Weighted Normals modifier. Thought currently (build from January 30) I believe these 2 don't work (at least as intended).