RFC: reducing wasted disk space from addon files

[Vincent Povirk]

I'm putting a note here mostly for completeness if someone finds the
thread later. I found this comment describing where addon .msi files
are searched:

    /*
     * Try to find addon .msi file in following order:
     * - directory stored in $dir_config_key value of
HKCU/Software/Wine/$config_key key
     * - $datadir/$addon_subdir/
     * - $INSTALL_DATADIR/wine/$addon_subdir/
     * - /usr/share/wine/$addon_subdir/
     * - download from URL stored in $url_config_key value of
HKCU/Software/Wine/$config_key key
     */

I think the simplest thing will be to duplicate this logic in mscoree,
except that mscoree will not do its own download. Instead of looking
for wine-mono-4.8.0.msi in those directories, mscoree will look for a
directory named wine-mono-4.8.0. If it doesn't find that directory in
any of the above locations, it will fall back on appwiz.cpl, which
will still look for a .msi in all of those places, downloading and
caching it if necessary, the way it does now.

That should cover everyone's use cases at least as well as the current
solution, and it won't require anyone building or packaging wine to
change anything. It will be necessary to replace the .msi with a
directory (built from the source tarball or extracted from a binary
tarball on winehq) if packagers want to take advantage of this work to
reduce prefix size.