Support new form of definitely non-nullable types: T & Any

^KT-26245 In Progress

compiler/testData/diagnostics/tests/explicitDefinitelyNotNullableViaIntersection/overrides.kt

@@ -0,0 +1,36 @@
+// !LANGUAGE: +DefinitelyNotNullTypeParameters
+
+interface A<T> {
+    fun foo(x: T): T
+    fun bar(x: T & Any): T & Any
+}
+
+interface B<T1> : A<T1> {
+    override fun foo(x: T1): T1
+    override fun bar(x: T1 & Any): T1 & Any
+}
+
+interface C<T2> : A<T2> {
+    <!NOTHING_TO_OVERRIDE!>override<!> fun foo(x: T2 & Any): T2 & Any
+    <!NOTHING_TO_OVERRIDE!>override<!> fun bar(x: T2): T2
+}
+
+interface D : A<String?> {
+    override fun foo(x: String?): String?
+    override fun bar(x: String): String
+}
+
+interface E : A<String> {
+    override fun foo(x: String): String
+    override fun bar(x: String): String
+}
+
+interface F : A<String?> {
+    <!NOTHING_TO_OVERRIDE!>override<!> fun foo(x: String): String
+    <!NOTHING_TO_OVERRIDE!>override<!> fun bar(x: String?): String?
+}
+
+interface G<T3 : Any> : A<T3> {
+    override fun foo(x: T3): T3
+    override fun bar(x: T3): T3
+}