fabric-*: require Fabric Loader 0.12.12

This is the release that includes all current log4j mitigation.
Changes in fabric.mod.json ensure the mod will completely refuse to load
unless it's on a fully patched Fabric server.

fabric-1.16.4/gradle.properties

@@ -4,7 +4,7 @@ org.gradle.jvmargs=-Xmx1G
 # check these on https://fabricmc.net/use
 minecraft_version=1.16.4
 yarn_mappings=1.16.4+build.6
-loader_version=0.10.6+build.214
+loader_version=0.12.12
 # Mod Properties
 archives_base_name=Dynmap
 # Dependencies