[wpilib] Add functional interface equivalents to MotorController (#6053)

This does not deprecate any current functionality, but prepares the way for future deprecation.

The drive classes now accept void(double) functions, which makes them more flexible.

The C++ API ended up a bit more verbose, but the Java API is really concise with method references, which is >80% of our userbase. For example:

`DifferentialDrive drive = new DifferentialDrive(m_leftMotor::set, m_rightMotor::set);`

Lambdas can be passed to interoperate with vendor motor controller APIs that don't have e.g., set(double), so CTRE doesn't have to maintain their WPI_ classes anymore.

MotorControllerGroup was replaced with PWMMotorController.addFollower() for PWM motor controllers. Users of CAN motor controllers should use their vendor's follower functionality.

wpilibjIntegrationTests/src/main/java/edu/wpi/first/wpilibj/fixtures/MotorEncoderFixture.java

@@ -22,6 +22,7 @@ import java.util.logging.Logger;
  * fixture. This allows tests to be mailable so that you can easily reconfigure the physical testbed
  * without breaking the tests.
  */
+@SuppressWarnings("removal")
 public abstract class MotorEncoderFixture<T extends MotorController> implements ITestFixture {
   private static final Logger logger = Logger.getLogger(MotorEncoderFixture.class.getName());
   private boolean m_initialized = false;