FIR: implement checker for open members

Specifically,

1. NON_FINAL_MEMBER_IN_FINAL_CLASS
2. NON_FINAL_MEMBER_IN_OBJECT

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

@@ -723,6 +723,18 @@ internal val KT_DIAGNOSTIC_CONVERTER = KtDiagnosticConverterBuilder.buildConvert
             token,
         )
     }
+    add(FirErrors.NON_FINAL_MEMBER_IN_FINAL_CLASS) { firDiagnostic ->
+        NonFinalMemberInFinalClassImpl(
+            firDiagnostic as FirPsiDiagnostic<*>,
+            token,
+        )
+    }
+    add(FirErrors.NON_FINAL_MEMBER_IN_OBJECT) { firDiagnostic ->
+        NonFinalMemberInObjectImpl(
+            firDiagnostic as FirPsiDiagnostic<*>,
+            token,
+        )
+    }
     add(FirErrors.MANY_COMPANION_OBJECTS) { firDiagnostic ->
         ManyCompanionObjectsImpl(
             firDiagnostic as FirPsiDiagnostic<*>,

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

@@ -515,6 +515,14 @@ sealed class KtFirDiagnostic<PSI: PsiElement> : KtDiagnosticWithPsi<PSI> {
         abstract val overriddenDeclaration: KtSymbol
     }
 
+    abstract class NonFinalMemberInFinalClass : KtFirDiagnostic<KtNamedDeclaration>() {
+        override val diagnosticClass get() = NonFinalMemberInFinalClass::class
+    }
+
+    abstract class NonFinalMemberInObject : KtFirDiagnostic<KtNamedDeclaration>() {
+        override val diagnosticClass get() = NonFinalMemberInObject::class
+    }
+
     abstract class ManyCompanionObjects : KtFirDiagnostic<PsiElement>() {
         override val diagnosticClass get() = ManyCompanionObjects::class
     }

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

@@ -822,6 +822,20 @@ internal class VarOverriddenByValImpl(
     override val firDiagnostic: FirPsiDiagnostic<*> by weakRef(firDiagnostic)
 }
 
+internal class NonFinalMemberInFinalClassImpl(
+    firDiagnostic: FirPsiDiagnostic<*>,
+    override val token: ValidityToken,
+) : KtFirDiagnostic.NonFinalMemberInFinalClass(), KtAbstractFirDiagnostic<KtNamedDeclaration> {
+    override val firDiagnostic: FirPsiDiagnostic<*> by weakRef(firDiagnostic)
+}
+
+internal class NonFinalMemberInObjectImpl(
+    firDiagnostic: FirPsiDiagnostic<*>,
+    override val token: ValidityToken,
+) : KtFirDiagnostic.NonFinalMemberInObject(), KtAbstractFirDiagnostic<KtNamedDeclaration> {
+    override val firDiagnostic: FirPsiDiagnostic<*> by weakRef(firDiagnostic)
+}
+
 internal class ManyCompanionObjectsImpl(
     firDiagnostic: FirPsiDiagnostic<*>,
     override val token: ValidityToken,