Add option to avoid clobbering visibility of <declare-styleable>

"aapt2 compile" marks styleables as public instead of preserving
information from <public/> or --visibility options.  This behavior can
now be disabled via --preserve-visibility-of-styleables.

Bug: 146649511
Change-Id: Ifb8ab396573d1393df737a59625e79e9cf2494a7
Tested: aapt2_tests
diff --git a/tools/aapt2/ResourceParser.cpp b/tools/aapt2/ResourceParser.cpp
index 45cea81..40eae54 100644
--- a/tools/aapt2/ResourceParser.cpp
+++ b/tools/aapt2/ResourceParser.cpp
@@ -1643,8 +1643,14 @@
                                            ParsedResource* out_resource) {
   out_resource->name.type = ResourceType::kStyleable;
 
-  // Declare-styleable is kPrivate by default, because it technically only exists in R.java.
-  out_resource->visibility_level = Visibility::Level::kPublic;
+  if (!options_.preserve_visibility_of_styleables) {
+    // This was added in change Idd21b5de4d20be06c6f8c8eb5a22ccd68afc4927 to mimic aapt1, but no one
+    // knows exactly what for.
+    //
+    // FWIW, styleables only appear in generated R classes.  For custom views these should always be
+    // package-private (to be used only by the view class); themes are a different story.
+    out_resource->visibility_level = Visibility::Level::kPublic;
+  }
 
   // Declare-styleable only ends up in default config;
   if (out_resource->config != ConfigDescription::DefaultConfig()) {