K2 scripting: add initial scripting support to K2 frontend

compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/FirTreeBuilder.kt

@@ -60,6 +60,7 @@ object FirTreeBuilder : AbstractFirTreeBuilder() {
     val backingField by element(Declaration, variable, typeParametersOwner, statement)
     val constructor by element(Declaration, function, typeParameterRefsOwner)
     val file by element(Declaration, declaration)
+    val script by element(Declaration, declaration)
     val packageDirective by element(Other)
 
     val anonymousFunction by element(Declaration, function, typeParametersOwner)

compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/NodeConfigurator.kt

@@ -451,6 +451,13 @@ object NodeConfigurator : AbstractFieldConfigurator<FirTreeBuilder>(FirTreeBuild
             +symbol("FirFileSymbol")
         }
 
+        script.configure {
+            +name
+            +fieldList(statement).withTransform()
+            +symbol("FirScriptSymbol")
+            +fieldList(contextReceiver)
+        }
+
         packageDirective.configure {
             +field("packageFqName", fqNameType)
         }