Following a request by Günter, we consider the document fonts (only rm
for now) when selecting an appropriate font encoding.
See #9741
The new default font encoding setting "auto" does
* consider the font encoding needed by the language(s), which can now
have fallback alternatives
* Consider which font encoding is provided by the document font
Thus, cm now will result in OT1 fontenc, if the language can deal with
that.
The font_enc pref is ditched: it is no longer needed.
The automatism is still very basic and is subject to extension.
File format and prefs format change.
Use the command as defined by Babel. This allows us to use the (more
advanced) Babel command if provided instead of rolling our own.
I add a dummy file format change in case it turns out we need to
do something here for old documents (e.g. with user preamble definitions)
