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.h

@@ -10,7 +10,6 @@
 #include <wpi/StringMap.h>
 #include <wpi/deprecated.h>
 
-#include "frc/smartdashboard/SendableBuilder.h"
 #include "frc/smartdashboard/SendableChooserBase.h"
 
 namespace frc {
@@ -112,7 +111,7 @@ class SendableChooser : public SendableChooserBase {
    */
   auto GetSelected() -> decltype(_unwrap_smart_ptr(m_choices[""]));
 
-  void InitSendable(SendableBuilder& builder) override;
+  void InitSendable(nt::NTSendableBuilder& builder) override;
 };
 
 }  // namespace frc