Desktop Heartbeat Logging - Log a heartbeat after app is created

[AlmostMatt]

Description

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On desktop, call LogHeartbeat after App is created. This should mean that heartbeats are consistently logged regardless of whether or not auth or firestore is included.

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Testing

Describe how you've tested these changes. Link any manually triggered Integration tests or CPP binary SDK Packaging Github Action workflows, if applicable.

Updated heartbeat controller and auth request unit tests to rely on this automatic call to LogHeartbeat instead of explicitly calling LogHeartbeat in those test cases.

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Type of Change

Place an x the applicable box:

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

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Notes

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• 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.