KT-6077 Compiler does not issue error on unsafe access to ArrayList with nullable values

#KT-6077 Fixed

compiler/testData/diagnostics/tests/platformTypes/methodCall/singleton.kt

@@ -4,5 +4,6 @@ trait Foo
 
 fun test() {
     var nullable: Foo? = null
-    val foo: Collection<Foo> = java.util.Collections.singleton(nullable)
+    val foo: Collection<Foo> = <!TYPE_MISMATCH!>java.util.Collections.singleton(nullable)<!>
+    val foo1: Collection<Foo> = java.util.Collections.singleton(nullable!!)
 }

compiler/testData/diagnostics/tests/platformTypes/nullableTypeArgument.kt

@@ -0,0 +1,9 @@
+import java.util.ArrayList
+
+fun foo() {
+    val list = ArrayList<String?>()
+
+    for (s in list) {
+        s<!UNSAFE_CALL!>.<!>length
+    }
+}

compiler/testData/diagnostics/tests/platformTypes/nullableTypeArgument.txt

@@ -0,0 +1,3 @@
+package
+
+internal fun foo(): kotlin.Unit