Move foreign annotation tests into diagnostics folder

third-party/java8-annotations/org/jspecify/nullness/Nullable.java

@@ -0,0 +1,14 @@
+package org.jspecify.nullness;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+import java.lang.annotation.ElementType;
+
+@Documented
+@Retention(RetentionPolicy.RUNTIME)
+@Target({ElementType.FIELD, ElementType.METHOD, ElementType.TYPE_USE, ElementType.PARAMETER})
+public @interface Nullable {
+
+}