[FIR] Add special node for elvis call

#KT-39074

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

@@ -287,6 +287,11 @@ object BuilderConfigurator : AbstractBuilderConfigurator<FirTreeBuilder>(FirTree
             useTypes(stubReferenceType)
         }
 
+        builder(elvisCall) {
+            default("calleeReference", "FirStubReference")
+            useTypes(stubReferenceType)
+        }
+
         builder(anonymousInitializer) {
             default("symbol", "FirAnonymousInitializerSymbol()")
         }

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

@@ -91,6 +91,7 @@ object FirTreeBuilder : AbstractFirTreeBuilder() {
     val qualifiedAccessWithoutCallee = element("QualifiedAccessWithoutCallee", Expression, statement)
     val qualifiedAccess = element("QualifiedAccess", Expression, qualifiedAccessWithoutCallee, resolvable)
     val checkNotNullCall = element("CheckNotNullCall", Expression, expression, call, resolvable)
+    val elvisCall = element("ElvisCall", Expression, expression, resolvable)
 
     val arrayOfCall = element("ArrayOfCall", Expression, expression, call)
     val arraySetCall = element("AugmentedArraySetCall", Expression, statement)

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

@@ -187,6 +187,11 @@ object NodeConfigurator : AbstractFieldConfigurator<FirTreeBuilder>(FirTreeBuild
             needTransformOtherChildren()
         }
 
+        elvisCall.configure {
+            +field("lhs", expression).withTransform()
+            +field("rhs", expression).withTransform()
+        }
+
         qualifiedAccessWithoutCallee.configure {
             +typeArguments.withTransform()
             +receivers