FIR: fix serialization of accessor with source-level annotations

compiler/testData/codegen/box/fir/NameHighlighter.kt

@@ -0,0 +1,27 @@
+// TARGET_BACKEND: JVM
+// MODULE: lib
+// FILE: NameHighlighter.kt
+
+object NameHighlighter {
+    var namesHighlightingEnabled = true
+        @TestOnly set
+}
+
+// FILE: TestOnly.java
+
+import java.lang.annotation.*;
+
+@Retention(RetentionPolicy.SOURCE)
+@Target({ElementType.METHOD, ElementType.CONSTRUCTOR})
+public @interface TestOnly {
+}
+
+// MODULE: main(lib)
+// FILE: main.kt
+
+fun box(): String {
+    if (!NameHighlighter.namesHighlightingEnabled) return "FAIL 1"
+    NameHighlighter.namesHighlightingEnabled = false
+    if (NameHighlighter.namesHighlightingEnabled) return "FAIL 2"
+    return "OK"
+}