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/livewindow/LiveWindow.h

@@ -7,9 +7,11 @@
 #include <functional>
 #include <memory>
 
-namespace frc {
-
+namespace wpi {
 class Sendable;
+}  // namespace wpi
+
+namespace frc {
 
 /**
  * The LiveWindow class is the public interface for putting sensors and
@@ -36,14 +38,14 @@ class LiveWindow {
    *
    * @param sendable component
    */
-  void EnableTelemetry(Sendable* component);
+  void EnableTelemetry(wpi::Sendable* component);
 
   /**
    * Disable telemetry for a single component.
    *
    * @param sendable component
    */
-  void DisableTelemetry(Sendable* component);
+  void DisableTelemetry(wpi::Sendable* component);
 
   /**
    * Disable ALL telemetry.