Do not always generate synthetic "$annotations" as private

Since annotations are a part of the declaration, they must have the same
visibility as the declaration in the bytecode. Otherwise obfuscators like
Proguard might strip the "$annotations" method and no annotations would be
found via Kotlin reflection

 #KT-15993 Fixed

compiler/testData/codegen/light-analysis/reflection/annotations/simpleValAnnotation.txt

@@ -9,6 +9,6 @@ public annotation class Simple {
 public final class SimpleValAnnotationKt {
     private final static field foo: int
     public final static @org.jetbrains.annotations.NotNull method box(): java.lang.String
-    private synthetic deprecated static @Simple method foo$annotations(): void
+    public synthetic deprecated static @Simple method foo$annotations(): void
     public final static method getFoo(): int
 }