Integrate serialization plugin into big Kotlin plugin

Split import handlers into multiple files
Add empty Maven handler for Android Studio

Add testRuntime dependency on kx-serialization-plugin for all modules which require compiler
plugins in test classpath

ultimate/ultimate-runner/build.gradle.kts

@@ -17,10 +17,9 @@ val intellijUltimateEnabled : Boolean by rootProject.extra
 
 val ideaUltimatePluginDir: File by rootProject.extra
 val ideaUltimateSandboxDir: File by rootProject.extra
-val serialPluginDir: File by rootProject.extra
 
 if (intellijUltimateEnabled) {
-    runIdeTask("runUltimate", ideaUltimatePluginDir, ideaUltimateSandboxDir, serialPluginDir) {
+    runIdeTask("runUltimate", ideaUltimatePluginDir, ideaUltimateSandboxDir) {
         dependsOn(":dist", ":ideaPlugin", ":ultimate:ideaUltimatePlugin")
     }
 }