Prohibit using null as a value of generic type

#KT-7350 Fixed
 #KT-7736 Fixed
 #KT-7485 Fixed

compiler/testData/diagnostics/tests/generics/nullability/nullToGeneric.kt

@@ -0,0 +1,35 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER,-UNUSED_VARIABLE,-BASE_WITH_NULLABLE_UPPER_BOUND
+
+fun <E> bar(x: E) {}
+
+fun <T> foo(): T {
+    val x1: T = <!NULL_FOR_NONNULL_TYPE!>null<!>
+    val x2: T? = null
+
+    bar<T>(<!NULL_FOR_NONNULL_TYPE!>null<!>)
+    bar<T?>(null)
+
+    return <!NULL_FOR_NONNULL_TYPE!>null<!>
+}
+
+fun <T> baz(): T? = null
+
+fun <T> foobar(): T = <!NULL_FOR_NONNULL_TYPE!>null<!>
+
+class A<F> {
+    fun xyz(x: F) {}
+
+    fun foo(): F {
+        val x1: F = <!NULL_FOR_NONNULL_TYPE!>null<!>
+        val x2: F? = null
+
+        xyz(<!NULL_FOR_NONNULL_TYPE!>null<!>)
+        bar<F?>(null)
+
+        return <!NULL_FOR_NONNULL_TYPE!>null<!>
+    }
+
+    fun baz(): F? = null
+
+    fun foobar(): F = <!NULL_FOR_NONNULL_TYPE!>null<!>
+}