refactor buildSrc scripts to root directory

buildSrc/src/main/kotlin/AddonConfig.kt

@@ -0,0 +1,41 @@
+import java.io.File
+import java.util.function.Predicate
+import org.gradle.api.Project
+import org.gradle.api.Task
+import org.gradle.jvm.tasks.Jar
+import org.gradle.kotlin.dsl.extra
+import kotlin.streams.asStream
+
+
+/**
+ * Configures a directory where addons will be put.
+ */
+fun Project.addonDir(dir: File, task: Task) {
+    task.doFirst {
+        dir.parentFile.mkdirs()
+        matchingAddons(dir) {
+            it.name.startsWith("Terra-") // Assume everything that starts with Terra- is a core addon.
+        }.forEach {
+            println("Deleting old addon: " + it.absolutePath)
+            it.delete()
+        }
+        forSubProjects(":common:addons") {
+            val jar = (tasks.named("jar").get() as Jar)
+            
+            val boot = if (extra.has("bootstrap") && extra.get("bootstrap") as Boolean) "bootstrap/" else ""
+            val target = File(dir, boot + jar.archiveFileName.get())
+            
+            val base = "${jar.archiveBaseName.get()}-${version}"
+            
+            println("Copying addon ${jar.archiveFileName.get()} to ${target.absolutePath}. Base name: $base")
+            
+            jar.archiveFile.orNull?.asFile?.copyTo(target)
+        }
+    }
+}
+
+fun matchingAddons(dir: File, matcher: Predicate<File>): Set<File> {
+    val matching = HashSet<File>()
+    dir.walk().asStream().filter(matcher).forEach(matching::add)
+    return matching
+}