[IR] Deserialize annotation classes as open

Compiler backend relies on the fact that all annotation classes have
OPEN modality. This is not the case for libraries that were compiled
before 1.6.20. 948dc4f3 fixes compatibility for Lazy IR, here we do the
same for IR deserializer.

^KT-51302 fixed

compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/IrDeclarationDeserializer.kt

@@ -12,7 +12,9 @@ import org.jetbrains.kotlin.backend.common.serialization.linkerissues.checkError
 import org.jetbrains.kotlin.backend.common.serialization.linkerissues.checkSymbolType
 import org.jetbrains.kotlin.backend.common.serialization.proto.IrDeclaration.DeclaratorCase.*
 import org.jetbrains.kotlin.backend.common.serialization.proto.IrType.KindCase.*
+import org.jetbrains.kotlin.descriptors.ClassKind
 import org.jetbrains.kotlin.descriptors.InlineClassRepresentation
+import org.jetbrains.kotlin.descriptors.Modality
 import org.jetbrains.kotlin.ir.IrBuiltIns
 import org.jetbrains.kotlin.ir.IrElement
 import org.jetbrains.kotlin.ir.declarations.*
@@ -308,6 +310,12 @@ class IrDeclarationDeserializer(
             checkSymbolType<IrClassSymbol>(symbol)
 
             val flags = ClassFlags.decode(fcode)
+            // Similar to 948dc4f3, compatibility hack for libs that were generated before 1.6.20.
+            val effectiveModality = if (flags.kind == ClassKind.ANNOTATION_CLASS) {
+                Modality.OPEN
+            } else {
+                flags.modality
+            }
             symbolTable.declareClass(signature, { symbol }) {
                 irFactory.createClass(
                     startOffset, endOffset, origin,
@@ -315,7 +323,7 @@ class IrDeclarationDeserializer(
                     deserializeName(proto.name),
                     flags.kind,
                     flags.visibility,
-                    flags.modality,
+                    effectiveModality,
                     flags.isCompanion,
                     flags.isInner,
                     flags.isData,