Add test case for codeanalysis annotation

compiler/testData/foreignAnnotationsJava8/tests/jspecify/defaults.kt

@@ -18,6 +18,8 @@ public class A {
 
     @DefaultNullable
     public String mixed(@NotNull String x) { return ""; }
+
+    public String explicitlyNullnessUnknown(@NullnessUnknown String x) { return ""; }
 }
 
 // FILE: main.kt
@@ -37,6 +39,10 @@ fun main(a: A) {
     a.mixed(<!NULL_FOR_NONNULL_TYPE!>null<!>)?.length
     a.mixed("")?.length
 
+    a.explicitlyNullnessUnknown("").length
+    a.explicitlyNullnessUnknown("")<!UNNECESSARY_SAFE_CALL!>?.<!>length
+    a.explicitlyNullnessUnknown(null).length
+
     a.defaultField<!UNNECESSARY_SAFE_CALL!>?.<!>length
     a.defaultField.length