Implement IPeripheral.getTarget on a few additional TEs

Also make it nullable. Hopefully this will allow us to distinguish
between non-default implementations more easily.

src/main/java/dan200/computercraft/api/peripheral/IPeripheral.java

@@ -81,10 +81,10 @@ default void detach( @Nonnull IComputerAccess computer )
      *
      * @return The object this peripheral targets
      */
-    @Nonnull
+    @Nullable
     default Object getTarget()
     {
-        return this;
+        return null;
     }
 
     /**

src/main/java/dan200/computercraft/shared/peripheral/commandblock/CommandBlockPeripheral.java

@@ -72,6 +72,13 @@ public boolean equals( IPeripheral other )
         return other != null && other.getClass() == getClass();
     }
 
+    @Nonnull
+    @Override
+    public Object getTarget()
+    {
+        return commandBlock;
+    }
+
     @Nonnull
     @Override
     public <T> LazyOptional<T> getCapability( @Nonnull Capability<T> cap, @Nullable Direction side )

src/main/java/dan200/computercraft/shared/peripheral/modem/wired/TileCable.java

@@ -114,6 +114,13 @@ public Vec3d getPosition()
             BlockPos pos = getPos().offset( modemDirection );
             return new Vec3d( pos.getX() + 0.5, pos.getY() + 0.5, pos.getZ() + 0.5 );
         }
+
+        @Nonnull
+        @Override
+        public Object getTarget()
+        {
+            return TileCable.this;
+        }
     };
     private LazyOptional<IPeripheral> modemCap;
 

src/main/java/dan200/computercraft/shared/peripheral/modem/wired/TileWiredModemFull.java

@@ -407,6 +407,13 @@ public Vec3d getPosition()
                 BlockPos pos = getPos().offset( side );
                 return new Vec3d( pos.getX() + 0.5, pos.getY() + 0.5, pos.getZ() + 0.5 );
             }
+
+            @Nonnull
+            @Override
+            public Object getTarget()
+            {
+                return TileWiredModemFull.this;
+            }
         };
     }
 }

src/main/java/dan200/computercraft/shared/peripheral/modem/wireless/TileWirelessModem.java

@@ -70,6 +70,13 @@ public boolean equals( IPeripheral other )
         {
             return this == other || (other instanceof Peripheral && entity == ((Peripheral) other).entity);
         }
+
+        @Nonnull
+        @Override
+        public Object getTarget()
+        {
+            return entity;
+        }
     }
 
     private final boolean advanced;

src/main/java/dan200/computercraft/shared/peripheral/monitor/MonitorPeripheral.java

@@ -14,6 +14,7 @@
 import dan200.computercraft.core.terminal.Terminal;
 
 import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 
 public class MonitorPeripheral extends TermMethods implements IPeripheral
 {
@@ -85,4 +86,11 @@ public boolean isColour() throws LuaException
     {
         return getMonitor().isColour();
     }
+
+    @Nullable
+    @Override
+    public Object getTarget()
+    {
+        return monitor;
+    }
 }

src/main/java/dan200/computercraft/shared/turtle/upgrades/CraftingTablePeripheral.java

@@ -44,4 +44,11 @@ public boolean equals( IPeripheral other )
     {
         return other instanceof CraftingTablePeripheral;
     }
+
+    @Nonnull
+    @Override
+    public Object getTarget()
+    {
+        return turtle;
+    }
 }