Support nullable callable references in FIR resolve

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

@@ -323,7 +323,7 @@ object ImplementationConfigurator : AbstractFirTreeImplementationConfigurator()
         }
 
         impl(resolvedQualifier) {
-            isMutable("packageFqName", "relativeClassFqName")
+            isMutable("packageFqName", "relativeClassFqName", "safe")
             default("classId") {
                 value = """
                     |relativeClassFqName?.let {

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

@@ -435,6 +435,7 @@ object NodeConfigurator : AbstractFieldConfigurator<FirTreeBuilder>(FirTreeBuild
             +field("packageFqName", fqNameType)
             +field("relativeClassFqName", fqNameType, nullable = true)
             +field("classId", classIdType, nullable = true)
+            +booleanField("safe")
             +typeArguments.withTransform()
         }