When chat scrolls, IDBearer URL menus shouldn't lead to the wrong place

Optimizes away multiple iterations over scroll lists and
multiple parsings of urls to determine the target(s)
At the cost of the last selection being stored statically in a vector

Removes virtual LFIDBearer::getNumSelected

indra/newview/llnameui.h

@@ -47,7 +47,6 @@ struct LLNameUI : public LFIDBearer
 	}
 
 	LLUUID getStringUUIDSelectedItem() const override final { return mNameID; }
-	S32 getNumSelected() const override final { return 1; }
 	Type getSelectedType() const override final { return mType; }
 
 	void setType(const Type& type);