[FE] Don't issue a deprecation warning for open val deferred init when the property is unconditionally effectively final

^KT-61228 Fixed
Review: https://jetbrains.team/p/kt/reviews/11694/timeline

compiler/testData/diagnostics/tests/backingField/OpenValDeferredInitError_InFinalClass_DisableEffectivelyFinal.kt

@@ -0,0 +1,29 @@
+// FIR_IDENTICAL
+// DIAGNOSTICS: -DEBUG_INFO_LEAKING_THIS
+// LANGUAGE:-TakeIntoAccountEffectivelyFinalInMustBeInitializedCheck
+// LANGUAGE:+ProhibitOpenValDeferredInitialization
+
+// Invalid combination of language feature flags. The user enabled 2.0 language flag (+ProhibitOpenValDeferredInitialization) and disabled
+// 1.9 language flag (-TakeIntoAccountEffectivelyFinalInMustBeInitializedCheck) => It's only possible if users manually set `-XXLanguage` =>
+// Technically, it's UB (undefined behaviour)
+//
+// On one hand, suppose that you have 1.9.0 compiler with -XXLanguage:-TakeIntoAccountEffectivelyFinalInMustBeInitializedCheck and then you
+// bump your compiler version to 1.9.20. It's not nice that you will get this compilation error considering that you didn't have a warning
+// => so probably we shouldn't report a error here
+//
+// But on the other hand, the error is expected by the combination of feature flags (we prohibit open val deferred initialization and
+// since we don't take effectively final into account) => we must be report a error
+//
+// Anyway, it's UB. Users shouldn't manually tune `-XXLanguage`
+
+interface Base {
+    val foo: Int
+}
+
+class Foo : Base {
+    <!MUST_BE_INITIALIZED_OR_FINAL_OR_ABSTRACT!>override val foo: Int<!>
+
+    init {
+        foo = 1
+    }
+}

compiler/testData/diagnostics/tests/backingField/OpenValDeferredInitError_InFinalClass_EnableEffectivelyFinal.kt

@@ -0,0 +1,15 @@
+// FIR_IDENTICAL
+// DIAGNOSTICS: -DEBUG_INFO_LEAKING_THIS
+// LANGUAGE:+TakeIntoAccountEffectivelyFinalInMustBeInitializedCheck
+// LANGUAGE:+ProhibitOpenValDeferredInitialization
+interface Base {
+    val foo: Int
+}
+
+class Foo : Base {
+    override val foo: Int
+
+    init {
+        foo = 1
+    }
+}

compiler/testData/diagnostics/tests/backingField/OpenValDeferredInitWarning_InFinalClass_DisableEffectivelyFinal.kt

@@ -0,0 +1,16 @@
+// FIR_IDENTICAL
+// DIAGNOSTICS: -DEBUG_INFO_LEAKING_THIS
+// LANGUAGE:-TakeIntoAccountEffectivelyFinalInMustBeInitializedCheck
+// LANGUAGE:-ProhibitOpenValDeferredInitialization
+// KT-61228 case
+interface Base {
+    val foo: Int
+}
+
+class Foo : Base {
+    override val foo: Int
+
+    init {
+        foo = 1
+    }
+}

compiler/testData/diagnostics/tests/backingField/OpenValDeferredInitWarning_InFinalClass_EnableEffectivelyFinal.kt

@@ -0,0 +1,15 @@
+// FIR_IDENTICAL
+// DIAGNOSTICS: -DEBUG_INFO_LEAKING_THIS
+// LANGUAGE:+TakeIntoAccountEffectivelyFinalInMustBeInitializedCheck
+// LANGUAGE:-ProhibitOpenValDeferredInitialization
+interface Base {
+    val foo: Int
+}
+
+class Foo : Base {
+    override val foo: Int
+
+    init {
+        foo = 1
+    }
+}