[Messaging] Change notification to allow same id

[a-maurice]

Description

Provide details of the change, and generalize the change in the PR title above.

To better align with how the underlying Android and iOS SDKs work, pass along the registration notification even if it is the same one that was sent earlier.

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Testing

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Type of Change

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• Bug fix. Add the issue # below if applicable.
• New feature. A non-breaking change which adds functionality.
• Other, such as a build process or documentation change.

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Notes

• Bug fixes and feature changes require an update to the Release Notes section of release_build_files/readme.md.
• Read the contribution guidelines CONTRIBUTING.md.
• Changes to the public API require an internal API review. If you'd like to help us make Firebase APIs better, please propose your change in a feature request so that we can discuss it together.

[gemini-code-assist]

Code Review

This pull request removes the early return check in NotifyListenerOnRegistrationReceived that prevented notifying the listener if the incoming registration ID matched the previous one. The reviewer suggested an optimization to avoid redundant string assignments when the registration ID remains unchanged, while still proceeding with the notification.

[gemini-code-assist]

Since we want to allow sending the registration notification even if it is the same as the previous one, we can still optimize the string assignment. If g_prev_registration_received already contains the same installationId, we can skip the redundant string copy/assignment while still proceeding to notify the listener.

  if (!g_prev_registration_received) {
    g_prev_registration_received = new std::string(installationId);
  } else if (*g_prev_registration_received != installationId) {
    *g_prev_registration_received = installationId;
  }