legacy chunk borders

backports the chunk border debug renderer introduced in 16w10a to 1.8.2 to 1.8.9 via legacy fabric

I verified support of optifabric / optifine on 1.8.9

requires loader 0.15+ (i think i lied, i set in the mod json but it's not using any mixinextras features now, so it can probably be safely overridden in a loader override if anyone cares)

it is activated via f3 + g, same as modern versions

MicrocontrollersDev made a forge version! (https://modrinth.com/mod/legacy-chunk-borders-forge)