Fix javadoc warnings (#2266)

Persuant to #1093, I added as many docstrings as I could, at least for
things I knew about. Some of the classes I just suppressed the Javadoc
warnings in because they aren't particularly useful to document. This
gets us down to less than 100 Javadoc warnings in total. Docs for core
classes on the C++ side were also added for parity.

photon-targeting/src/main/java/org/photonvision/targeting/MultiTargetPNPResult.java

@@ -30,8 +30,11 @@ public class MultiTargetPNPResult
     private static final int MAX_IDS = 32;
 
     public PnpResult estimatedPose = new PnpResult();
+
+    /** The fiducial IDs used to calculate this multi-target result. */
     public List<Short> fiducialIDsUsed = List.of();
 
+    /** Used for serialization and tests. */
     public MultiTargetPNPResult() {}
 
     public MultiTargetPNPResult(PnpResult results, List<Short> ids) {
@@ -72,9 +75,10 @@ public class MultiTargetPNPResult
                 + "]";
     }
 
+    /** MultiTargetPNPResult protobuf for serialization. */
     public static final MultiTargetPNPResultProto proto = new MultiTargetPNPResultProto();
 
-    // tODO!
+    /** MultiTargetPNPResult PhotonStruct for serialization. */
     public static final MultiTargetPNPResultSerde photonStruct = new MultiTargetPNPResultSerde();
 
     @Override