[Fontconfig] Can't enable any bitmap fonts except Fixed, Unifont and WQY

[Weiwu Zhang]

In the past decade, enabling bitmap is as easy as linking
70-force-bitmaps.conf in /etc/fonts/conf.d while removing any
references to 70-no-bitmaps.conf

Since 18.04 however, this would not give the user all bitmap
fonts. The only fonts that appear in fc-cache(1) with this technique
are Fixed, Unifont, Wqy (bitmap song). All of the typical ones like
Helvetica, Times, Lucida would not show up.

Not sure if this is a font-config issue or my Ubuntu 18.04. I surely
did both `sudo dpkg-reconfigure fontconfig` per Ubuntu requirement and
`sudo fc-cache -f -v` per font-config requirement.

I also suspected the location of the font files,
/usr/share/fonts/X11/100dpi, isn't indexed by
font-config. Coincidently, all the missing fonts like Times, Helvetica
and Lucida are in this director. I tried to eliminate this probable
cause by copying the files to ~/.fonts and saw no change to
fc-list(1).

Since Fixed, Unifont, Wqy-Bitmap are all typical fonts used in a
terminal emulator and "Helvetica, Times, Lucida" all do not fit
terminal emulators, there seem to be a second probable cause: an
artificial bias towards not allowing bitmaps in places other than
terminals.

Thanks a lot for advices.