Add MixinExtras on 1.16.4+

We'll use it in 1.20 mixins.
Unclear what minimal fabric-loader version it requires, so in the interest of
keeping older versions compatible with OptiFabric (old versions of which aren't
compatible with the latest fabric-loader), we'll add it to 1.16.4+ only.

versions/1.17.1/src/main/resources/fabric.mod.json

@@ -29,7 +29,8 @@
       "com.replaymod.render.utils.FlawlessFrames::registerConsumer"
     ],
     "preLaunch": [
-      "com.replaymod.core.DummyChainLoadEntryPoint"
+      "com.replaymod.core.DummyChainLoadEntryPoint",
+      "com.replaymod.core.MixinExtrasInit"
     ],
     "mm:early_risers": [
       "com.replaymod.core.ReplayModMMLauncher"