[NI] Discard DefNotNull types inside invariant positions

#KT-30297 Fixed
 #KT-32168 Fixed
 #KT-27722 Fixed (actually, it was fixed with addition of DefNotNullTypes, and now test was added to save this behavior)
 #KT-32345 Fixed

compiler/testData/diagnostics/tests/inference/constraints/definitelyNotNullTypeInvariantPosition.kt

@@ -0,0 +1,24 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER -UNUSED_EXPRESSION
+
+class Inv<T>(val x: T?)
+
+fun <K> create(y: K) = Inv(y)
+fun <K> createPrivate(y: K) = Inv(y)
+
+fun takeInvInt(i: Inv<Int>) {}
+
+fun <S> test(i: Int, s: S) {
+    val a = Inv(s)
+
+    <!DEBUG_INFO_EXPRESSION_TYPE("Inv<S>")!>a<!>
+
+    val b = create(i)
+
+    <!DEBUG_INFO_EXPRESSION_TYPE("Inv<kotlin.Int>")!>b<!>
+
+    val c = createPrivate(i)
+
+    <!DEBUG_INFO_EXPRESSION_TYPE("Inv<kotlin.Int>")!>c<!>
+
+    takeInvInt(create(i))
+}

compiler/testData/diagnostics/tests/inference/constraints/definitelyNotNullTypeInvariantPosition.txt

@@ -0,0 +1,14 @@
+package
+
+public fun </*0*/ K> create(/*0*/ y: K): Inv<K>
+public fun </*0*/ K> createPrivate(/*0*/ y: K): Inv<K>
+public fun takeInvInt(/*0*/ i: Inv<kotlin.Int>): kotlin.Unit
+public fun </*0*/ S> test(/*0*/ i: kotlin.Int, /*1*/ s: S): kotlin.Unit
+
+public final class Inv</*0*/ T> {
+    public constructor Inv</*0*/ T>(/*0*/ x: T?)
+    public final val x: T?
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}

compiler/testData/diagnostics/tests/inference/constraints/wrongApproximationWithDefNotNullTypesAndDelegates.kt

@@ -0,0 +1,15 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+
+import kotlin.reflect.KProperty
+
+class Foo {
+    var test: String by refreshOnUpdate("str")
+
+    fun <T> refreshOnUpdate(initialValue: T) = RefreshDelegate(initialValue)
+
+    class RefreshDelegate<T>(initialValue: T?) {
+        operator fun getValue(thisRef: Foo, property: KProperty<*>): T = TODO()
+
+        operator fun setValue(thisRef: Foo, property: KProperty<*>, value: T) {}
+    }
+}

compiler/testData/diagnostics/tests/inference/constraints/wrongApproximationWithDefNotNullTypesAndDelegates.txt

@@ -0,0 +1,19 @@
+package
+
+public final class Foo {
+    public constructor Foo()
+    public final var test: kotlin.String
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public final fun </*0*/ T> refreshOnUpdate(/*0*/ initialValue: T): Foo.RefreshDelegate<T>
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+
+    public final class RefreshDelegate</*0*/ T> {
+        public constructor RefreshDelegate</*0*/ T>(/*0*/ initialValue: T?)
+        public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+        public final operator fun getValue(/*0*/ thisRef: Foo, /*1*/ property: kotlin.reflect.KProperty<*>): T
+        public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+        public final operator fun setValue(/*0*/ thisRef: Foo, /*1*/ property: kotlin.reflect.KProperty<*>, /*2*/ value: T): kotlin.Unit
+        public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+    }
+}