[USD EXPORT] USD Exporter does not export subsequence data from the master sequence

As described in the steps to reproduce, when exporting a selected binding somwehere in a sequence hierarchy into usd, the export yields an empty result when using 'selection only' option. The export works correctly when the subsequence itself is opened, however then we lose the information on transforms contained in the camera root from an another subsequence.

The result export as of now should have no timesamples or no camera prim whatsoever, but the correct result should have the transforms given by the camera root from the example, not only the transforms given from the keyframes of the camera subsequence.

The issue should be the same even for a subsequence track instead of a shot track.

In the repro of this issue, there are assets in the Content folder:

'seq' as the master sequence

'subseq' as the camera sequence

'rootseq' as the camera root sequence

Steps to Reproduce

1. Create a master level sequence.
2. Create two subsequences
   1. 'rootseq' containing a root actor placed somewhere in the scene
   2. 'camseq' containing a CineCameraActor
3. In the master sequence, create a shot track and add the 'camseq' subsequence
4. Add the 'rootseq' as a subsequence track
5. Click into 'camseq' and create an attach track to the root actor in 'rootseq', add abritrary transforms and keyframes into the sequence
6. Select the camera in 'masterseq' > 'camseq' and export the binding as USD(A) with the seqeunece settings 'selection only'=True.