[kotlin2cpg] Fix assertion error by locking descriptorRenderer options

DescriptorRendererImpl asserts that the options are locked upon init. This means that the type rendering will fail anywhere with assertions enabled (`-ea`) as the options weren't being locked after setup.

joern-cli/frontends/kotlin2cpg/build.sbt

@@ -23,4 +23,5 @@ libraryDependencies ++= Seq(
 
 enablePlugins(JavaAppPackaging, LauncherJarPlugin)
 trapExit := false
-Test / fork := false
+Test / fork := true
+Test / javaOptions ++= Seq("-ea")

joern-cli/frontends/kotlin2cpg/src/main/scala/io/joern/kotlin2cpg/types/TypeRenderer.scala

@@ -44,6 +44,7 @@ class TypeRenderer(val keepTypeArguments: Boolean = false) {
  case _: ErrorType => cpgUnresolvedType
  case t => t
  }
+ opts.lock()
  new DescriptorRendererImpl(opts)
  }