Frostiful for Minecraft 1.21.9

Frostiful is now updated to Minecraft 1.21.9. Per the LTS policy, Minecraft 1.21.6-8 are now unsupported.

Please note that this version does not work on 1.21.10! Because of this, 1.21.9 will not be supported for very long, as I will quickly be moving on 1.21.10. I am just waiting on Cloth Config to release an update for 1.21.10.

Also, because of large-scale rendering changes made in this version, this version is released as a beta. Some things may not be working properly, please report any issues you find to the GitHub issue tracker, or to my discord. Thank you for your patience and understanding.