impl(storage): remove deprecated ClientOptions class

[mpeddada1]

Removes ClientOptions class. Also removes some deprecated storage Client constructors that use ClientOptions.
Note that the entire client_options.cc haven't been removed yet because:

1. ApplyPolicies is still being used in client.h
2. RestEndpoint and IamEndpoint are still used in google/cloud/storage/internal/rest/stub.cc

TODO: Add migration guide.

These will be removed in a follow-up PR.

[gemini-code-assist]

Summary of Changes

Hello @mpeddada1, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request completes the deprecation process for the ClientOptions and ChannelOptions classes within the storage client library. It involves a comprehensive refactoring to migrate all client configuration and credential management to the unified google::cloud::Options class. This change simplifies the API, removes redundant code, and aligns the storage client with the broader google-cloud-cpp library's approach to option management. Some helper functions previously associated with ClientOptions remain in client_options.h for continued use, with their full removal planned for a subsequent PR.

Highlights

• Removal of Deprecated Classes: The ClientOptions and ChannelOptions classes, previously marked as deprecated, have been entirely removed from the codebase.
• Migration to Unified Options: All client configurations, including credentials, endpoints, and policy application, now exclusively utilize the more general google::cloud::Options class, streamlining option handling across the library.
• Deprecated Constructor and Method Removal: Several Client constructors and static factory methods that relied on the old ClientOptions have been removed, simplifying the client's public interface.
• Refactored Credential Handling: Functions related to OAuth2 credentials (e.g., AuthorizedUserCredentials, ServiceAccountCredentials, GoogleDefaultCredentials) have been updated to directly accept and use google::cloud::Options, eliminating the need for ChannelOptions.

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[gemini-code-assist]

Code Review

This pull request primarily focuses on removing the deprecated ClientOptions and ChannelOptions classes, transitioning the google::cloud::storage library to use the unified google::cloud::Options system. Key changes include deleting ClientOptions and ChannelOptions definitions and their associated methods and constructors across various client, connection, and credential-related files. The Client::CreateDefaultClient() static method was removed, and client initialization now directly uses google::cloud::Options. Credentials handling, specifically SigningEmail and SignBlobImpl, were updated to retrieve options from connection_->options() instead of connection_->client_options(). Test files were refactored to remove ClientOptions usage and related mocks. Review comments highlighted redundant header includes (google/cloud/storage/client_options.h and google/cloud/options.h) and a compilation error in an integration test due to a Client(Options{}) constructor returning Client instead of StatusOr<Client>, and incorrect pointer usage with UseClient.

[gemini-code-assist]

Client(Options{}) returns a Client object, not a StatusOr<Client>. The ASSERT_THAT(client, IsOk()) will not compile. Also, UseClient expects a Client, not a Client*.

  auto client = Client(Options{});
  ASSERT_NO_FATAL_FAILURE(
      UseClient(client, bucket_name(), MakeRandomObjectName(), LoremIpsum()));

[gemini-code-assist]

This include seems unnecessary after the refactoring. The Client class no longer directly uses any types from client_options.h.

[gemini-code-assist]

The header google/cloud/storage/options.h already includes google/cloud/options.h, so this include is redundant.

[gemini-code-assist]

The header google/cloud/storage/options.h already includes google/cloud/options.h, so this include is redundant.

[gemini-code-assist]

This include seems unnecessary. The file does not appear to use any symbols from client_options.h.