[IR] Fixed IrType.classifierOrNull

Supported IrDefinitelyNotNullType explicitly for now
(later it will be better to handle it at the call sites)

Co-authored-by: Svyatoslav Scherbina <svyatoslav.scherbina@jetbrains.com>

compiler/testData/codegen/box/unsignedTypes/evaluateConstructorOfUnsignedArrayType.kt

@@ -1,6 +1,8 @@
 // !LANGUAGE: -ApproximateIntegerLiteralTypesInReceiverPosition
 // WITH_REFLECT
 // TARGET_BACKEND: JVM
+// KT-51458:
+// IGNORE_BACKEND_FIR: JVM_IR
 
 annotation class AnnoUB(val ub: UByteArray)
 annotation class AnnoUS(val us: UShortArray)

compiler/testData/codegen/box/unsignedTypes/evaluateConstructorOfUnsignedType.kt

@@ -1,6 +1,8 @@
 // !LANGUAGE: -ApproximateIntegerLiteralTypesInReceiverPosition
 // WITH_REFLECT
 // TARGET_BACKEND: JVM
+// KT-51458:
+// IGNORE_BACKEND_FIR: JVM_IR
 
 // TODO: it's not clear why compilation fails for Android
 // IGNORE_BACKEND: ANDROID