FIR serializer: throw exception on getting ConeIntegerLiteralType

This commit assumes that ILTs are forbidden
at the end of resolve, at least in public API

compiler/fir/fir-serialization/src/org/jetbrains/kotlin/fir/serialization/FirElementSerializer.kt

@@ -592,8 +592,7 @@ class FirElementSerializer private constructor(
                 }
             }
             is ConeDefinitelyNotNullType,
-            is ConeIntersectionType,
+            is ConeIntersectionType -> {
-            is ConeIntegerLiteralType -> {
                 val approximatedType = if (toSuper) {
                     typeApproximator.approximateToSuperType(type, TypeApproximatorConfiguration.PublicDeclaration)
                 } else {
@@ -604,6 +603,9 @@ class FirElementSerializer private constructor(
                 }
                 return typeProto(approximatedType as ConeKotlinType)
             }
+            is ConeIntegerLiteralType -> {
+                throw IllegalStateException("Integer literal types should not persist up to the serializer: ${type.render()}")
+            }
             is ConeCapturedType -> {
                 throw IllegalStateException("Captured types should not persist up to the serializer: ${type.render()}")
             }