console.lua: default to --osd-font without completions

Currently --osd-font is the default for select, and a monospace font is
the default for free-form text mode. We can also default to the
proportional --osd-font for mp.input.get clients that don't specify
completions and thus don't need alignment, which is most clients.

In builtin scripts, this is the case for filtering stats key bindings.