Add GetNextAction API so that a caller that might want to implement an event driven mechanism to drive the BDX transfer can get the next output event from the TransferSession on demand

Currently we have the PollOutput API where the expectation is the caller needs to poll frequently for the next output event from the TransferSession which introduces a delay based on the
poll interval in handling every single BDX message or transfer session event handled by the caller.

Author: nivi-apple

src/protocols/bdx/BdxTransferSession.cpp

@@ -134,6 +134,11 @@ void TransferSession::PollOutput(OutputEvent & event, System::Clock::Timestamp c
     mPendingOutput = OutputEventType::kNone;
 }
 
+void TransferSession::GetNextAction(OutputEvent & event)
+{
+    PollOutput(event, System::SystemClock().GetMonotonicTimestamp());
+}
+
 CHIP_ERROR TransferSession::StartTransfer(TransferRole role, const TransferInitData & initData, System::Clock::Timeout timeout)
 {
     VerifyOrReturnError(mState == TransferState::kUnitialized, CHIP_ERROR_INCORRECT_STATE);

src/protocols/bdx/BdxTransferSession.h

@@ -165,6 +165,24 @@ class DLL_EXPORT TransferSession
      */
     void PollOutput(OutputEvent & event, System::Clock::Timestamp curTime);
 
+    /**
+     * @brief
+     *   Gets the pending output event from the transfer session in the event param passed in by the caller.
+     *   The output event may contain some data for the caller to act upon.
+     *
+     *   It is possible that consecutive calls to this method may emit different outputs depending on the state of the
+     *   TransferSession object and so we need to call this until we get an event of type - OutputEventType::kNone
+     *
+     *   Note that if the event type is kMsgToSend, the caller is expected to send the message immediately over the
+     *   exchange otherwise the caller is expected to pass the event to HandleTransferSessionOutput to handle the BDX
+     *   message or any other TransferSession event.
+     *
+     *   See OutputEventType for all possible output event types.
+     *
+     * @param event     Reference to an OutputEvent struct that will be filled out with any pending output event data
+     */
+    void GetNextAction(OutputEvent & event);
+
     /**
      * @brief
      *   Initializes the TransferSession object and prepares a TransferInit message (emitted via PollOutput()).