* Extract vcpkg_extract_archive from vcpkg_find_acquire_program.
* Extract vcpkg_download_sourceforge from vcpkg_from_sourceforge.
This allows vcpkg_find_acquire_program to download from SourceForge without needing to temporarily change _VCPKG_EDITABLE.
* Use whether a URI is known for an entity to decide whether to downloads it rather than checking a separate supported_on_unix boolean.
* Add unparsed arguments check to vcpkg_extract_archive
