Font rendering: enable ligatures

[kenokenobingo]

It’d be nice to have ligature support for fonts like Fira Code.

[neeasade]

https://st.suckless.org/patches/ligatures/

[tynanbe]

st.suckless.org/patches/ligatures

Here's a patch I made after combining st-ligatures-boxdraw-0.8.3 with st-ligatures-alpha-scrollback-0.8.3 and applying the changes to xst.

It appears that these highlighted lines in my gist were missing from PR #104, though I haven't tested whether their addition resolves the issues with boxdraw.

Anyone interested, please feel free to use the patch to create a new PR~

[tynanbe]

Initial impressions are good; however, I have encountered an issue where many alpha characters overlap when using Victor Mono Nerd Font italic variants (cursive). I switched to a custom build of Iosevka anyway, but the problem should probably be looked at further; it could be a fault of the patch or it could be something wonky with that particular font. The symptom does not manifest without the patch.