Sort sealed class inheritors to ensure reproducible builds with IC

without this sorting the inheritors field in the metadata may depend on
whether some inheritors are compiled in the IC round or not.

compiler/fir/tree/src/org/jetbrains/kotlin/fir/declarations/SealedClassInheritors.kt

@@ -36,7 +36,7 @@ fun FirRegularClass.getSealedClassInheritors(session: FirSession): List<ClassId>
 @OptIn(SealedClassInheritorsProviderInternals::class)
 fun FirRegularClass.setSealedClassInheritors(inheritors: List<ClassId>) {
     require(this.isSealed)
-    sealedInheritorsAttr = inheritors
+    sealedInheritorsAttr = inheritors.sortedBy { it.asFqNameString() }
 }
 
 private object SealedClassInheritorsKey : FirDeclarationDataKey()