font: render with pango for better fontconfig support

[rtgiskard]

cairo_select_font_face() does not support fontconfig fallback, use pango instead

for my case, I'm using a local font config like this:

<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<fontconfig>
	<match target="pattern">
		<test name="family" qual="any"><string>sans-serif</string></test>
		<edit name="family" mode="prepend" binding="strong">
			<string>Symbols Nerd Font</string>
			<string>Inconsolata</string>
			<string>LXGW WenKai Mono</string>
		</edit>
	</match>
</fontconfig>

The symbol only nerd font is the first to match, and then the others as fallback, this works well for my other applications, without the need to install many other nerd patched fonts.

But this setup will cause slurp -d to show numbers as all block

[tmccombs]

Would it be possible to make pango an optional dependency instead of a required one?