[commands] Enhance Command Sendable implementations (#4822)

wpilibNewCommands/src/main/native/cpp/frc2/command/ParallelDeadlineGroup.cpp

@@ -4,6 +4,8 @@
 
 #include "frc2/command/ParallelDeadlineGroup.h"
 
+#include <wpi/sendable/SendableBuilder.h>
+
 using namespace frc2;
 
 ParallelDeadlineGroup::ParallelDeadlineGroup(
@@ -93,3 +95,10 @@ void ParallelDeadlineGroup::SetDeadline(std::unique_ptr<Command>&& deadline) {
   AddRequirements(m_deadline->GetRequirements());
   m_runWhenDisabled &= m_deadline->RunsWhenDisabled();
 }
+
+void ParallelDeadlineGroup::InitSendable(wpi::SendableBuilder& builder) {
+  CommandBase::InitSendable(builder);
+
+  builder.AddStringProperty(
+      "deadline", [this] { return m_deadline->GetName(); }, nullptr);
+}