[Suggestion] Generate -bex parameter for .bex files loaded through the Mods section

[Berzasperd]

This is a suggestion for built-in support for Boom Extended files in the same manner as Dehacked files are handled. This is a very low priority suggestion, as these patches are usually incorporated into the .wad and loaded by the sourceport / engine. This change would be almost entirely for legacy support for old maps or specific engines, but I feel it would still improve the user experience.

As of now, a simple workaround is to just use the additional command line arguments field to load such files, as DoomRunner will incorporate the -bex parameter into the final launch command as reliably as any other command.

To complete this addition, the file selection window that appears when adding a mod (the + button) would need the .bex file extension added to the list of defaults. As of now, the files can still be selected if the user changes the selection to All Files (*) but they will generate a -file parameter instead of -bex.

[Youda008]

added to the recent hotfix release