[commands] Merge CommandBase into Command and SubsystemBase into Subsystem (#5392)

Moves all CommandBase functionality into Command and deprecates CommandBase for removal.
Moves all SubsystemBase functionality into Subsystem and deprecates SubsystemBase for removal.
Adds a function to CommandScheduler to remove all registered Subsystems.

wpilibNewCommands/src/main/native/include/frc2/command/SubsystemBase.h

@@ -4,11 +4,7 @@
 
 #pragma once
 
-#include <string>
-#include <string_view>
-
-#include <wpi/sendable/Sendable.h>
-#include <wpi/sendable/SendableHelper.h>
+#include <wpi/deprecated.h>
 
 #include "frc2/command/Subsystem.h"
 
@@ -18,51 +14,13 @@ namespace frc2 {
  * provides a more intuitive method for setting the default command.
  *
  * This class is provided by the NewCommands VendorDep
+ *
+ * @deprecated All functionality provided by SubsystemBase has been merged into
+ * Subsystem. Use Subsystem instead.
  */
-class SubsystemBase : public Subsystem,
-                      public wpi::Sendable,
-                      public wpi::SendableHelper<SubsystemBase> {
- public:
-  void InitSendable(wpi::SendableBuilder& builder) override;
-
-  /**
-   * Gets the name of this Subsystem.
-   *
-   * @return Name
-   */
-  std::string GetName() const;
-
-  /**
-   * Sets the name of this Subsystem.
-   *
-   * @param name name
-   */
-  void SetName(std::string_view name);
-
-  /**
-   * Gets the subsystem name of this Subsystem.
-   *
-   * @return Subsystem name
-   */
-  std::string GetSubsystem() const;
-
-  /**
-   * Sets the subsystem name of this Subsystem.
-   *
-   * @param name subsystem name
-   */
-  void SetSubsystem(std::string_view name);
-
-  /**
-   * Associate a Sendable with this Subsystem.
-   * Also update the child's name.
-   *
-   * @param name name to give child
-   * @param child sendable
-   */
-  void AddChild(std::string name, wpi::Sendable* child);
-
+class [[deprecated("Use Subsystem instead")]] SubsystemBase : public Subsystem {
  protected:
+  WPI_DEPRECATED("Use Subsystem instead")
   SubsystemBase();
 };
 }  // namespace frc2