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/smartdashboard/SendableChooser.inc

@@ -11,6 +11,8 @@
 #include <utility>
 #include <vector>
 
+#include <networktables/NTSendableBuilder.h>
+
 #include "frc/smartdashboard/SendableChooser.h"
 
 namespace frc {
@@ -44,7 +46,7 @@ auto SendableChooser<T>::GetSelected()
 }
 
 template <class T>
-void SendableChooser<T>::InitSendable(SendableBuilder& builder) {
+void SendableChooser<T>::InitSendable(nt::NTSendableBuilder& builder) {
   builder.SetSmartDashboardType("String Chooser");
   builder.GetEntry(kInstance).SetDouble(m_instance);
   builder.AddStringArrayProperty(