Improve class name generation for scripts and REPL snippets

- allow to override default name/scheme
- implement host/engine specific names for jsr223 to avoid classloading
  clashes (also fix "eval in eval" test)

plugins/scripting/scripting-compiler-impl/src/org/jetbrains/kotlin/scripting/definitions/ScriptDefinition.kt

@@ -31,6 +31,7 @@ abstract class ScriptDefinition : UserDataHolderBase() {
     abstract fun isScript(file: File): Boolean
     abstract val fileExtension: String
     abstract val name: String
+    open val defaultClassName: String = "Script"
     // TODO: used in settings, find out the reason and refactor accordingly
     abstract val definitionId: String
 
@@ -138,6 +139,9 @@ abstract class ScriptDefinition : UserDataHolderBase() {
                 compilationConfiguration[ScriptCompilationConfiguration.displayName]?.takeIf { it.isNotBlank() }
                     ?: compilationConfiguration[ScriptCompilationConfiguration.baseClass]!!.typeName.substringAfterLast('.')
 
+        override val defaultClassName: String
+            get() = compilationConfiguration[ScriptCompilationConfiguration.defaultIdentifier] ?: super.defaultClassName
+
         override val definitionId: String get() = compilationConfiguration[ScriptCompilationConfiguration.baseClass]!!.typeName
 
         override val contextClassLoader: ClassLoader? by lazy {

plugins/scripting/scripting-compiler-impl/src/org/jetbrains/kotlin/scripting/resolve/refineCompilationConfiguration.kt

@@ -291,7 +291,7 @@ fun SourceCode.getVirtualFile(definition: ScriptDefinition): VirtualFile {
         val vFile = LocalFileSystem.getInstance().findFileByIoFile(file)
         if (vFile != null) return vFile
     }
-    val scriptName = withCorrectExtension(name ?: "script", definition.fileExtension)
+    val scriptName = withCorrectExtension(name ?: definition.defaultClassName, definition.fileExtension)
     val scriptPath = when (this) {
         is FileScriptSource -> file.path
         is ExternalSourceCode -> externalLocation.toString()