[FIR] Add a class representing the old syntax contract description in order to use the previous class for the new syntax

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

@@ -154,6 +154,7 @@ object FirTreeBuilder : AbstractFirTreeBuilder() {
     val effectDeclaration = element("EffectDeclaration", Contracts)
 
     val contractDescription = element("ContractDescription", Contracts)
+    val legacyRawContractDescription = element("LegacyRawContractDescription", Contracts, contractDescription)
     val rawContractDescription = element("RawContractDescription", Contracts, contractDescription)
     val resolvedContractDescription = element("ResolvedContractDescription", Contracts, contractDescription)
 }

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

@@ -610,13 +610,17 @@ object NodeConfigurator : AbstractFieldConfigurator<FirTreeBuilder>(FirTreeBuild
         }
 
         rawContractDescription.configure {
-            +field("contractCall", functionCall)
+            +fieldList("rawEffects", expression)
         }
 
         resolvedContractDescription.configure {
             +fieldList("effects", effectDeclaration)
             +fieldList("unresolvedEffects", statement)
         }
+
+        legacyRawContractDescription.configure {
+            +field("contractCall", functionCall)
+        }
     }
 }