[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/externalJavaAnnotation.kt

@@ -0,0 +1,19 @@
+// SKIP_WHEN_OUT_OF_CONTENT_ROOT
+// FILE: usage.kt
+<expr>
+fun test() = ClassWithExternalAnnotatedMembers().externalNotNullMethod()
+</expr>
+
+// FILE: ClassWithExternalAnnotatedMembers.java
+public class ClassWithExternalAnnotatedMembers {
+    public String externalNotNullMethod() {
+        return "";
+    }
+}
+
+// FILE: annotations.xml
+<root>
+    <item name='ClassWithExternalAnnotatedMembers java.lang.String externalNotNullMethod()'>
+        <annotation name='org.jetbrains.annotations.NotNull'/>
+    </item>
+</root>