[commands] Add DeferredCommand (#5566)

Allows commands to be constructed at runtime without proxying.

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

@@ -142,6 +142,16 @@ CommandPtr Select(std::function<Key()> selector,
   return SelectCommand(std::move(selector), std::move(vec)).ToPtr();
 }
 
+/**
+ * Runs the command supplied by the supplier.
+ *
+ * @param supplier the command supplier
+ * @param requirements the set of requirements for this command
+ */
+[[nodiscard]]
+CommandPtr Defer(wpi::unique_function<CommandPtr()> supplier,
+                 Requirements requirements);
+
 /**
  * Constructs a command that schedules the command returned from the supplier
  * when initialized, and ends when it is no longer scheduled. The supplier is