mpremote: Copy empty sub-dirs with "mpremote fs cp -r dir :".

[glenn20]

Ensure "mpremote fs cp -r dir :" creates empty sub-dirs on the remote.

Currently, empty sub-directories are skipped during a recursive copy from the local filesystem.

This PR ensure that empty sub-directories are re-created on the remote device.

[github-actions]

Code size report:

   bare-arm:    +0 +0.000% 
minimal x86:    +0 +0.000% 
   unix x64:    +0 +0.000% standard
      stm32:    +0 +0.000% PYBV10
        rp2:    +0 +0.000% PICO

[jimmo]

I have included a fix for the same issue in #11777

[glenn20]

Closing for #11777 .