FileSystem.Unix.File.Move uses "rename" in more cases (dotnet/corefx#40611)
* FileSystem.Unix.File.Move use rename in more cases, avoid link/copy when possible, improve performance on file systems that do not support hard links, such as FAT
* Adapt Unit Tests for accounting FileSystemWatcher events fired by FileSystem.Unix.File.Move implementation that use rename in more cases, avoiding link/copy when possible
Commit migrated from https://github.com/dotnet/corefx/commit/
89b087ba5548338bb604db4e1cca0e42f8273e2b