Delegate RefRight category filtering to ProjectState

Allow the ProjectState class to implement the filtering of each
RefRight instance by category, rather than repeating the logic
in the classes that use them.  This opens the door for the state
to cache the filtered collections at some later point in time,
and may help accelerate common action category lookups like for
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Change-Id: I6ddddd031afe59fc04c4226a01d656cca14277d0
Signed-off-by: Shawn O. Pearce <sop@google.com>
3 files changed