Extracts the compressed file from the gzip archive.
async gzip.extract(): Promise<void>
Invoking Extract decompresses the archive specified by ArchiveFile. The compressed file will be extracted, and written to disk. Also, FileCompressedName will be set to the filename found in the archive.
If a filename (i.e., FileCompressedName) is stored in the gzip headers, this filename will be used.
Otherwise, if ArchiveFile ends in ".gz", this filename, less the ".gz" extension will be used. If there are multiple files in the archive, the current 0-based file index will be appended to all files after the first file to differentiate between multiple files. For instance "test.gz" would become "test" for the first file and "test.gz" would become "test.1" for the second file in the archive.
If neither of these two conditions holds, ".unzipped" will be appended to ArchiveFile.