Implement script instance capturing in script lowering

for regular classes only. Reimplementing the main behavior of the
old BE and implementing few cases on top of it.
#KT-19423 fixed

compiler/tests-for-compiler-generator/tests/org/jetbrains/kotlin/test/generators/GenerateJUnit3CompilerTests.kt

@@ -107,7 +107,7 @@ fun generateJUnit3CompilerTests(args: Array<String>) {
             }
 
             testClass<AbstractScriptCodegenTest> {
-                model("codegen/script", extension = "kts")
+                model("codegen/script", extension = "kts", targetBackend = TargetBackend.JVM)
             }
 
             testClass<AbstractCustomScriptCodegenTest> {