Fixed inconsistent behavior when calling CreateCopyOfAsync from interface instead of extension method. The overwrite: false throw check now happens inside of CreateCopyOfFallbackAsync.
Fix inconsistent CreateCopyOfAsync behavior in SystemFolder when a file exist and overwrite: false is given.
Fixed an issue where calling MemoryFile.OpenStreamAsync wouldn't return a stream with a 0 position, and would keep position the same even after outer disposal by other callers.
Renamed test class names to include most derived tested type.