filesystem provider does not support fileMappings

[jimmylewis]

Describe the bug

Using the new fileMappings feature with the filesystem provider does not filter the files correctly.

To Reproduce

{
  "version": "3.0",
  "defaultProvider": "unpkg",
  "defaultDestination": "Scripts/",
  "libraries": [
    {
      "library": "SourcePath/",
      "provider": "filesystem",
      "fileMappings": [
        {
          "files": ["*.css"]
        }
      ]
    }
  ]
}

Run libman restore, see that all files from the source folder get copied (not just the *.css files in the filter).

Expected behavior

Only files matching the fileMapping should get copied