R1:4a98e0ff65a4

Allow Owners packages to be configured to ignore generated paths in Differential

Summary:
Depends on D19427. Ref T13130. See PHI251. Support configuring owners packages so they ignore generated paths.

This is still a little rough. A couple limitations:

- It's hard to figure out how to use this control if you don't know what it's for, but we don't currently have a "CheckboxesEditField". I may add that soon.
- The attribute ignore list doesn't apply to Diffusion, only Differential, which isn't obvious.