Split Fabric Rendering API support code into an optional module

[jellysquid3]

Right now, the development of Sodium for Minecraft 1.21.4 is blocked on upstream's port of Fabric Rendering API. We need to find a way to make this dependency optional so that we can get unblocked and avoid delays in the future.

The work involved to do this looks to be significant, and there is no way it can be done in the next day. As a stop-gap solution, we may need to distribute a patched version of the upstream module so that we can release on time.

To be clear, the goal is simply to make it so that Fabric integration is not required for our team to work on a prototype port of the mod. We don't plan to change our stance regarding Fabric API support whatsoever.

[jellysquid3]

Fabric API has a very large outstanding pull request (FabricMC/fabric#4247) that is being actively updated, which Sodium is currently targeting in a snapshot branch. But there were some breaking changes made today that we still need to adapt for, and there are not yet any reviews.

[jellysquid3]

Pepper let me know that they are expecting to be able to merge the pull request today, which would unblock things.

[jellysquid3]

Fabric API 0.110.5 has been released, which should allow us to complete our port. I will reduce the priority of this issue as a result.