vconsole: allow to control font scaling

This adds FONT_SCALE= setting in vconsole.conf,
vconsole.font_scale= kernel command line option and credential support.
When 2 or 200% is specified, the console font size will be doubled.

Closes #43273.

man/systemd.system-credentials.xml

@@ -340,10 +340,12 @@
         <term><varname>vconsole.font</varname></term>
         <term><varname>vconsole.font_map</varname></term>
         <term><varname>vconsole.font_unimap</varname></term>
+        <term><varname>vconsole.font_scale</varname></term>
         <listitem>
           <para>Console settings to apply, see
           <citerefentry><refentrytitle>systemd-vconsole-setup.service</refentrytitle><manvolnum>8</manvolnum></citerefentry> for details.</para>
 
+          <para><varname>vconsole.font_scale</varname> was added in version 262.</para>
           <xi:include href="version-info.xml" xpointer="v253"/>
         </listitem>
       </varlistentry>