Add helper functions to cxx::filesystem

[elfenpiff]

Brief feature description

In unit tests we sometimes require platform independent helper functions to modify directories. We should add functions like:

Required

• create_directory
• temp_directory_path (used for file lock and sockets)
• remove & remove_all

Optionally also:

• exists
• is_directory
• is_regular_file
• is_socket

It is important that those functions are working platform independently!

ToDo

• Implement required features
• Implement optional features
• When this is implemented tests to the FileLock have to be added, see: iox-#1036 builder pattern for file lock #1418 (comment)