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/SendableChooserBase.h

@@ -7,12 +7,11 @@
 #include <atomic>
 #include <string>
 
+#include <networktables/NTSendable.h>
 #include <networktables/NetworkTableEntry.h>
 #include <wpi/SmallVector.h>
 #include <wpi/mutex.h>
-
-#include "frc/smartdashboard/Sendable.h"
-#include "frc/smartdashboard/SendableHelper.h"
+#include <wpi/sendable/SendableHelper.h>
 
 namespace frc {
 
@@ -22,8 +21,8 @@ namespace frc {
  * It contains static, non-templated variables to avoid their duplication in the
  * template class.
  */
-class SendableChooserBase : public Sendable,
-                            public SendableHelper<SendableChooserBase> {
+class SendableChooserBase : public nt::NTSendable,
+                            public wpi::SendableHelper<SendableChooserBase> {
  public:
   SendableChooserBase();
   ~SendableChooserBase() override = default;