All data uploaded in root cache (empty layer caches) on Windows

[rcowsill]

Describe the bug
In jobs running on windows, the code that splits out the layers into separate caches is bypassed. All the layer content is left in the root cache. Separated layer caches are created, but each one only contains an empty folder.

To Reproduce
Can be seen in the CI workflow of this repo.

The root cache is 96MB:
https://github.com/satackey/action-docker-layer-caching/runs/1515471574?check_suite_focus=true#step:6:83

Notice that all the layer caches are 30 bytes:
https://github.com/satackey/action-docker-layer-caching/runs/1515471574?check_suite_focus=true#step:6:132

Expected behavior
Layer files are moved out of the root cache and saved in their own layer cache.

Runner Environment (please complete the following information):

• OS: Microsoft Windows Server 2019 10.0.17763 Datacenter
• Action version: v0.0.10

Additional context
It looks like this is caused by the \ directory separators used on Windows. recursive-readdir returns paths with \ on Windows, but moveLayerTarsInDir expects /.