[C++][Dataset] Do not ignore file paths with underscore/dot when full path was specified

Currently, when passing a list of file path to FileSystemDatasetFactory, the files that have one of their parent directories with a underscore or dot are skipped. Since the file paths were passed as an explicit list, we should maybe not skip them.

For example, when specifying a directory (Selector), it will only check child directories to skip, not parent directories.