[commands] Update Command documentation (NFC) (#3881)

Add reference to which VendorDep the class is included in.
Add missing OldCommands C++ Documentation (copied from Java).

wpilibNewCommands/src/main/native/include/frc2/command/MecanumControllerCommand.h

@@ -47,6 +47,8 @@ namespace frc2 {
  * <p>The robot angle controller does not follow the angle given by
  * the trajectory but rather goes to the angle given in the final state of the
  * trajectory.
+ *
+ * This class is provided by the NewCommands VendorDep
  */
 class MecanumControllerCommand
     : public CommandHelper<CommandBase, MecanumControllerCommand> {