Add support for RxJava's nullability annotations.

compiler/testData/foreignAnnotations/tests/rxjava.kt

@@ -0,0 +1,42 @@
+// !DIAGNOSTICS: -UNUSED_VARIABLE -UNUSED_PARAMETER
+// FILE: A.java
+
+import io.reactivex.annotations.*;
+
+public class A<T> {
+    @Nullable public String field = null;
+
+    @Nullable
+    public String foo(@NonNull String x, @Nullable CharSequence y) {
+        return "";
+    }
+
+    @NonNull
+    public String bar() {
+        return "";
+    }
+
+    @Nullable
+    public T baz(@NonNull T x) { return x; }
+}
+
+// FILE: main.kt
+
+fun main(a: A<String>, a1: A<String?>) {
+    a.foo("", null)?.length
+    a.foo("", null)<!UNSAFE_CALL!>.<!>length
+    a.foo(<!NULL_FOR_NONNULL_TYPE!>null<!>, "")<!UNSAFE_CALL!>.<!>length
+
+    a.bar().length
+    a.bar()<!UNNECESSARY_NOT_NULL_ASSERTION!>!!<!>.length
+
+    a.field?.length
+    a.field<!UNSAFE_CALL!>.<!>length
+
+    a.baz("")<!UNSAFE_CALL!>.<!>length
+    a.baz("")?.length
+    a.baz(<!NULL_FOR_NONNULL_TYPE!>null<!>)<!UNSAFE_CALL!>.<!>length
+
+    a1.baz("")!!.length
+    a1.baz(<!NULL_FOR_NONNULL_TYPE!>null<!>)!!.length
+}