[commands] Update Command documentation (NFC) (#3881)

Add reference to which VendorDep the class is included in.
Add missing OldCommands C++ Documentation (copied from Java).

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

@@ -10,6 +10,8 @@ namespace frc2 {
 /**
  * Class that holds scheduling state for a command.  Used internally by the
  * CommandScheduler
+ *
+ * This class is provided by the NewCommands VendorDep
  */
 class CommandState final {
  public: