[FIR] add tests on external annotations

Tests are excluded in COMPILED_JAVA mode because in this
mode external annotations are not present at all

^KT-62310

analysis/low-level-api-fir/testData/getOrBuildFir/wholeDeclaration/notNullJavaAnnotation.kt

@@ -0,0 +1,15 @@
+// SKIP_WHEN_OUT_OF_CONTENT_ROOT
+// FILE: usage.kt
+<expr>
+fun test() = ClassWithExternalAnnotatedMembers().notNullMethod()
+</expr>
+
+// FILE: ClassWithExternalAnnotatedMembers.java
+import org.jetbrains.annotations.NotNull;
+
+public class ClassWithExternalAnnotatedMembers {
+    @NotNull
+    public String notNullMethod() {
+        return "";
+    }
+}