Migrate more prints and graphics.len calls to font::

I especially focused on graphics.len and the print calls around them,
because graphics.len calls appear a bit less often, might be overlooked
when migrating print calls (thus possibly using different fonts by
accident) and are often used for some kind of right-alignment or
centering which can be changed into PR_RIGHT or PR_CEN with a different
X anyway.

Notably, I also added a new function to generate these kinds of
sliders: ....[]............

Different languages means that the slider for analogue stick
sensitivity needs to be longer to fit possibly long words for
Low/Medium/High, and then different font sizes means that the longer
slider won't fit onscreen in a language that needs a 12-wide font. So
slider_get() can take a "target width", which dynamically changes the
number of characters depending on the width of them in the interface
font.

I kinda forgot that I could force the 8x8 font instead of adapting the
characters in the slider to the font, and other ideas (like using
different characters or a more graphical progress bar) have been
brought up on Discord, so this might all change again sooner or later.

desktop_version/src/main.cpp

@@ -891,6 +891,8 @@ static void unfocused_run(void)
     {
         graphics.fill_rect(0, 0, 0);
 #define FLIP(YPOS) graphics.flipmode ? 232 - YPOS : YPOS
+        /* The pause screen can also appear on the language screen, where highlighting
+         * a language changes the used language metadata but not the loaded strings... */
         uint32_t flags = PR_CEN | PR_BOR | PR_FONT_IDX(loc::langmeta.font_idx);
         font::print(flags | PR_CJK_HIGH, -1, FLIP(110), loc::gettext("Game paused"), 196 - help.glow, 255 - help.glow, 196 - help.glow);
         font::print(flags | PR_CJK_LOW, -1, FLIP(120), loc::gettext("[click to resume]"), 196 - help.glow, 255 - help.glow, 196 - help.glow);