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/PowerDistributionPanel.h

@@ -5,20 +5,18 @@
 #pragma once
 
 #include <hal/Types.h>
-
-#include "frc/smartdashboard/Sendable.h"
-#include "frc/smartdashboard/SendableHelper.h"
+#include <wpi/sendable/Sendable.h>
+#include <wpi/sendable/SendableHelper.h>
 
 namespace frc {
 
-class SendableBuilder;
-
 /**
  * Class for getting voltage, current, temperature, power and energy from the
  * CAN PDP.
  */
-class PowerDistributionPanel : public Sendable,
-                               public SendableHelper<PowerDistributionPanel> {
+class PowerDistributionPanel
+    : public wpi::Sendable,
+      public wpi::SendableHelper<PowerDistributionPanel> {
  public:
   /**
    * Constructs a PowerDistributionPanel.
@@ -96,7 +94,7 @@ class PowerDistributionPanel : public Sendable,
    */
   int GetModule() const;
 
-  void InitSendable(SendableBuilder& builder) override;
+  void InitSendable(wpi::SendableBuilder& builder) override;
 
  private:
   hal::Handle<HAL_PDPHandle> m_handle;