meson subprojects update --reset now re-extract tarballs

When using --reset option, the source tree of [wrap-file] subprojects is now deleted and re-extracted from cached tarballs, or re-downloaded. This is because Meson has no way to know if the source tree or the wrap file has been modified, and --reset should guarantee that latest code is being used on next reconfigure.

Use --reset with caution if you do local changes on non-git subprojects.