Python interface: File path corruption on Windows

File paths with \ sent from python side ends up as a path with the \ removed on C++ side most likely due to "feature" in PdmFieldScriptingCapabilityIOHandler.

Seems to happen with lists of paths, not single path parameters.

Workaround is to use pathlib.PurePath.as_posix() on Python side to get a path with only / before sending the paths to ResInsight. 