Properly handle REPL snippets with exceptions ...

so the REPL remain operational after exception in one of the snippets:
- separately return script class and script instance on evaluation (
  because in case of an exception the class is valid, while the instance
  is not).
- store both the class and the instance in the history
- handle this data accordingly

libraries/scripting/jvm-host-test/test/kotlin/script/experimental/jvmhost/test/ReplTest.kt

@@ -80,9 +80,11 @@ class ReplTest : TestCase() {
             simpleScriptompilationConfiguration,
             simpleScriptEvaluationConfiguration,
             sequenceOf(
-                "throw RuntimeException(\"abc\")"
+                "throw RuntimeException(\"abc\")",
+                "val x = 3",
+                "x + 1"
             ),
-            sequenceOf(RuntimeException("abc"))
+            sequenceOf(RuntimeException("abc"), null, 4)
         )
     }
 
@@ -107,11 +109,12 @@ class ReplTest : TestCase() {
                     }
                 }
                 .onSuccess {
-                    it.returnValue.scriptInstance?.let { snippetInstance ->
-                        currentEvalConfig = ScriptEvaluationConfiguration(currentEvalConfig) {
-                            previousSnippets.append(snippetInstance)
+                    val snippetClass = it.returnValue.scriptClass
+                    currentEvalConfig = ScriptEvaluationConfiguration(currentEvalConfig) {
+                        previousSnippets.append(it.returnValue.scriptInstance)
+                        if (snippetClass != null) {
                             jvm {
-                                baseClassLoader(snippetInstance::class.java.classLoader)
+                                baseClassLoader(snippetClass.java.classLoader)
                             }
                         }
                     }