R1:7f98a8575d0a

Allow different policy rules for different types of objects

Summary:
Ref T5681. Policy rules can now select objects they can apply to, so a rule like "task author" only shows up where it makes sense (when defining task policies).

This will let us define rules like "members of thread" in Conpherence, "subscribers", etc., to make custom policies more flexible.

Notes:

- Per D13251, we need to do a little work to get the right options for policies like "Maniphest > Default View Policy". This should allow…