libcamera: request: Declare a using directive for map of buffers

Declare a using directive for the map of Stream to FrameBuffer. Update
all users of Request::buffers() to use the new usage directive.

Signed-off-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/libcamera/request.cpp

@@ -37,6 +37,11 @@ LOG_DEFINE_CATEGORY(Request)
  * The request has been cancelled due to capture stop
  */
 
+/**
+ * \typedef Request::BufferMap
+ * \brief A map of Stream to FrameBuffer pointers
+ */
+
 /**
  * \class Request
  * \brief A frame capture request