Split Sendable into NT and non-NT portions (#3432)

The non-NT portion has been moved to wpiutil.
The NT portion has been moved to ntcore (as NTSendable).

SendableBuilder similarly split and moved.

SendableRegistry moved to wpiutil.

In C++, SendableHelper also moved to wpiutil.

This enables use of Sendable from wpimath and also enables
moving several classes from wpilib to wpimath.

wpilibc/src/main/native/include/frc/Relay.h

@@ -8,15 +8,13 @@
 #include <string>
 
 #include <hal/Types.h>
+#include <wpi/sendable/Sendable.h>
+#include <wpi/sendable/SendableHelper.h>
 
 #include "frc/MotorSafety.h"
-#include "frc/smartdashboard/Sendable.h"
-#include "frc/smartdashboard/SendableHelper.h"
 
 namespace frc {
 
-class SendableBuilder;
-
 /**
  * Class for Spike style relay outputs.
  *
@@ -30,8 +28,8 @@ class SendableBuilder;
  * a solenoid).
  */
 class Relay : public MotorSafety,
-              public Sendable,
-              public SendableHelper<Relay> {
+              public wpi::Sendable,
+              public wpi::SendableHelper<Relay> {
  public:
   enum Value { kOff, kOn, kForward, kReverse };
   enum Direction { kBothDirections, kForwardOnly, kReverseOnly };
@@ -93,7 +91,7 @@ class Relay : public MotorSafety,
 
   std::string GetDescription() const override;
 
-  void InitSendable(SendableBuilder& builder) override;
+  void InitSendable(wpi::SendableBuilder& builder) override;
 
  private:
   int m_channel;