Update so many dependencies, merge Forge/Fabric for final jar (#1651)

* Update so many dependencies, merge Forge/Fabric for final

* Clean up contrib docs for Gradle change

* Fix setting compat flags while using toolchain

* Fix deprecation in doc printer

* Restore proper forge JAR name

* Add dist classifier for mod jar

* Properly relocate new bStats

* Fix jar used from fabric

* Fix fabric bom

* Dup the shaded classes for consistency

* Sync Forge/Fabric log4j versions, de-dup

* Downgrade both log4j. This will work

* Update some plugins as well

* Drop the fabric force stuff

* Use duplicate strategy to directly merge jar

buildSrc/src/main/kotlin/CommonConfig.kt

@@ -1,5 +1,9 @@
 import org.gradle.api.Project
+import org.gradle.api.plugins.JavaPluginExtension
+import org.gradle.jvm.toolchain.JavaLanguageVersion
+import org.gradle.kotlin.dsl.dependencies
 import org.gradle.kotlin.dsl.repositories
+import org.gradle.kotlin.dsl.the
 
 fun Project.applyCommonConfiguration() {
     group = rootProject.group
@@ -50,4 +54,29 @@ fun Project.applyCommonConfiguration() {
             cacheChangingModulesFor(5, "MINUTES")
         }
     }
+
+    plugins.withId("java") {
+        the<JavaPluginExtension>().toolchain {
+            languageVersion.set(JavaLanguageVersion.of(8))
+        }
+    }
+
+    dependencies {
+        constraints {
+            for (conf in configurations.names) {
+                add(conf, "com.google.guava:guava") {
+                    version { strictly(Versions.GUAVA) }
+                    because("Mojang provides Guava")
+                }
+                add(conf, "com.google.code.gson:gson") {
+                    version { strictly(Versions.GSON) }
+                    because("Mojang provides Gson")
+                }
+                add(conf, "it.unimi.dsi:fastutil") {
+                    version { strictly(Versions.FAST_UTIL) }
+                    because("Mojang provides FastUtil")
+                }
+            }
+        }
+    }
 }