aconfig: add support for local override

1, add a new field in storage metadata proto, for each container, there
is a local override file.

2, update write api to expose the api to map a writable file given the
specific path. the cannonical api will require a storage metadata proto,
and then find the right file path and map it.

3, minor update to make the proto lib cc_library instead of
cc_library_static

Bug: b/312444587
Test: atest -c
Change-Id: Iaf0aff44c1ca3ad4bffc5e06bb99bb276b9069c5

tools/aconfig/aconfig_storage_file/Android.bp

@@ -56,7 +56,7 @@ rust_protobuf {
     min_sdk_version: "29",
 }
 
-cc_library_static {
+cc_library {
     name: "libaconfig_storage_protos_cc",
     proto: {
         export_proto_headers: true,

tools/aconfig/aconfig_storage_file/protos/aconfig_storage_metadata.proto

@@ -27,7 +27,8 @@ message storage_file_info {
   optional string flag_map = 4;
   optional string flag_val = 5;
   optional string flag_info = 6;
-  optional int64 timestamp = 7;
+  optional string local_overrides = 7;
+  optional int64 timestamp = 8;
 }
 
 message storage_files {

tools/aconfig/aconfig_storage_write_api/aconfig_storage_write_api.cpp

@@ -66,8 +66,31 @@ static Result<std::string> find_storage_file(
   return Error() << "Unable to find storage files for container " << container;
 }
 
+
+namespace private_internal_api {
+
+/// Get mutable mapped file implementation.
+Result<MutableMappedStorageFile> get_mutable_mapped_file_impl(
+    std::string const& pb_file,
+    std::string const& container,
+    StorageFileType file_type) {
+  if (file_type != StorageFileType::flag_val &&
+      file_type != StorageFileType::flag_info) {
+    return Error() << "Cannot create mutable mapped file for this file type";
+  }
+
+  auto file_result = find_storage_file(pb_file, container, file_type);
+  if (!file_result.ok()) {
+    return Error() << file_result.error();
+  }
+
+  return map_mutable_storage_file(*file_result);
+}
+
+} // namespace private internal api
+
 /// Map a storage file
-static Result<MutableMappedStorageFile> map_storage_file(std::string const& file) {
+Result<MutableMappedStorageFile> map_mutable_storage_file(std::string const& file) {
   struct stat file_stat;
   if (stat(file.c_str(), &file_stat) < 0) {
     return ErrnoError() << "stat failed";
@@ -97,28 +120,6 @@ static Result<MutableMappedStorageFile> map_storage_file(std::string const& file
   return mapped_file;
 }
 
-namespace private_internal_api {
-
-/// Get mutable mapped file implementation.
-Result<MutableMappedStorageFile> get_mutable_mapped_file_impl(
-    std::string const& pb_file,
-    std::string const& container,
-    StorageFileType file_type) {
-  if (file_type != StorageFileType::flag_val &&
-      file_type != StorageFileType::flag_info) {
-    return Error() << "Cannot create mutable mapped file for this file type";
-  }
-
-  auto file_result = find_storage_file(pb_file, container, file_type);
-  if (!file_result.ok()) {
-    return Error() << file_result.error();
-  }
-
-  return map_storage_file(*file_result);
-}
-
-} // namespace private internal api
-
 /// Get mutable mapped file
 Result<MutableMappedStorageFile> get_mutable_mapped_file(
     std::string const& container,

tools/aconfig/aconfig_storage_write_api/include/aconfig_storage/aconfig_storage_write_api.hpp

@@ -26,6 +26,10 @@ Result<MutableMappedStorageFile> get_mutable_mapped_file_impl(
 
 } // namespace private_internal_api
 
+/// Map a storage file
+Result<MutableMappedStorageFile> map_mutable_storage_file(
+    std::string const& file);
+
 /// Get mapped writeable storage file
 Result<MutableMappedStorageFile> get_mutable_mapped_file(
     std::string const& container,