Bleed px in Blender 2.8

It's in the texture paint options, meaning 2 locations:

1. The 3D View "Tool Settings" which appears above the header. This is sometimes hidden so you may need to reveal it. The options menu is all the way to the far right of the tool settings:
   
2. Alternatively you can access these same settings in a vertical layout (same as 2.79) in the Active Tool & Workspace Settings: