Use wpi::span instead of wpi::ArrayRef across all libraries (#3414)

- Remove ArrayRef.h
- Add SpanExtras.h for a couple of convenience functions

wpilibNewCommands/src/main/native/include/frc2/command/button/Trigger.h

@@ -9,7 +9,7 @@
 #include <memory>
 #include <utility>
 
-#include <wpi/ArrayRef.h>
+#include <wpi/span.h>
 
 #include "frc2/command/Command.h"
 #include "frc2/command/CommandScheduler.h"
@@ -101,7 +101,7 @@ class Trigger {
    * @paaram requirements the required subsystems.
    */
   Trigger WhenActive(std::function<void()> toRun,
-                     wpi::ArrayRef<Subsystem*> requirements = {});
+                     wpi::span<Subsystem* const> requirements = {});
 
   /**
    * Binds a command to be started repeatedly while the trigger is active, and
@@ -161,7 +161,7 @@ class Trigger {
    * @param requirements the required subsystems.
    */
   Trigger WhileActiveContinous(std::function<void()> toRun,
-                               wpi::ArrayRef<Subsystem*> requirements = {});
+                               wpi::span<Subsystem* const> requirements = {});
 
   /**
    * Binds a command to be started when the trigger becomes active, and
@@ -261,7 +261,7 @@ class Trigger {
    * @param requirements the required subsystems.
    */
   Trigger WhenInactive(std::function<void()> toRun,
-                       wpi::ArrayRef<Subsystem*> requirements = {});
+                       wpi::span<Subsystem* const> requirements = {});
 
   /**
    * Binds a command to start when the trigger becomes active, and be canceled