Use a version script for libaconfig_storage_read_api_cc

Restrict the set of exported symbols to those in the aconfig_storage
namespace by way of a version script. This shrinks the shared lib size
by ~75%, from ~800KB to <200KB.

Bug: 336657207
Test: m
Change-Id: I56044fe667a713cf1d94f96c992f379a5725850f

tools/aconfig/aconfig_storage_read_api/Android.bp

@@ -102,8 +102,6 @@ cc_library {
         "//apex_available:anyapex",
     ],
     min_sdk_version: "29",
+    version_script: "libaconfig_storage_read_api_cc.map",
     double_loadable: true,
-    cflags: [
-        "-fvisibility=hidden",
-    ],
 }

tools/aconfig/aconfig_storage_read_api/libaconfig_storage_read_api_cc.map

@@ -0,0 +1,11 @@
+LIBACONFIG_STORAGE_READ_API_CC {
+  # Export everything in the aconfig_storage namespace. This includes both the
+  # public API and library internals.
+  global:
+    extern "C++" {
+        aconfig_storage::*;
+    };
+  # Hide everything else.
+  local:
+    *;
+};