[FIR] Report UNSUPPORTED_SEALED_FUN_INTERFACE

^KT-59957 Fixed

analysis/analysis-api-fir/src/org/jetbrains/kotlin/analysis/api/fir/diagnostics/KtFirDataClassConverters.kt

@@ -650,6 +650,12 @@ internal val KT_DIAGNOSTIC_CONVERTER = KtDiagnosticConverterBuilder.buildConvert
             token,
         )
     }
+    add(FirErrors.UNSUPPORTED_SEALED_FUN_INTERFACE) { firDiagnostic ->
+        UnsupportedSealedFunInterfaceImpl(
+            firDiagnostic as KtPsiDiagnostic,
+            token,
+        )
+    }
     add(FirErrors.SUPERTYPE_NOT_A_CLASS_OR_INTERFACE) { firDiagnostic ->
         SupertypeNotAClassOrInterfaceImpl(
             firDiagnostic.a,

analysis/analysis-api-fir/src/org/jetbrains/kotlin/analysis/api/fir/diagnostics/KtFirDiagnostics.kt

@@ -497,6 +497,10 @@ sealed interface KtFirDiagnostic<PSI : PsiElement> : KtDiagnosticWithPsi<PSI> {
         override val diagnosticClass get() = ClassInheritsJavaSealedClass::class
     }
 
+    interface UnsupportedSealedFunInterface : KtFirDiagnostic<PsiElement> {
+        override val diagnosticClass get() = UnsupportedSealedFunInterface::class
+    }
+
     interface SupertypeNotAClassOrInterface : KtFirDiagnostic<KtElement> {
         override val diagnosticClass get() = SupertypeNotAClassOrInterface::class
         val reason: String

analysis/analysis-api-fir/src/org/jetbrains/kotlin/analysis/api/fir/diagnostics/KtFirDiagnosticsImpl.kt

@@ -584,6 +584,11 @@ internal class ClassInheritsJavaSealedClassImpl(
     token: KtLifetimeToken,
 ) : KtAbstractFirDiagnostic<KtTypeReference>(firDiagnostic, token), KtFirDiagnostic.ClassInheritsJavaSealedClass
 
+internal class UnsupportedSealedFunInterfaceImpl(
+    firDiagnostic: KtPsiDiagnostic,
+    token: KtLifetimeToken,
+) : KtAbstractFirDiagnostic<PsiElement>(firDiagnostic, token), KtFirDiagnostic.UnsupportedSealedFunInterface
+
 internal class SupertypeNotAClassOrInterfaceImpl(
     override val reason: String,
     firDiagnostic: KtPsiDiagnostic,