dataconnect: DataConnectCredentialsTokenManager: initialize synchronously to fix race condition

[dconeybe]

This PR changes the initialization of Data Conect's "Auth" and "AppCheck" mechanisms to be more synchronous. Not only does this fix a bug introduced a few commits ago by #6446 but also simplifies the logic and reduces the amount of non-determinism.

The race condition fixed by this PR manifested only on on my MacBook laptop (not on my Linux workstation) and is simply due to arbitrary thread scheduling differences. One such test failure looked like this:

failed: collect_gets_notified_of_per_data_deserializer_successes(com.google.firebase.dataconnect.QuerySubscriptionIntegrationTest)
java.lang.IllegalStateException: getToken() cannot be called before initialize()
	at com.google.firebase.dataconnect.core.DataConnectCredentialsTokenManager.getToken(DataConnectCredentialsTokenManager.kt:322)
	at com.google.firebase.dataconnect.core.DataConnectGrpcMetadata.get(DataConnectGrpcMetadata.kt:80)
	at com.google.firebase.dataconnect.core.DataConnectGrpcRPCs.executeMutation(DataConnectGrpcRPCs.kt:142)
	at com.google.firebase.dataconnect.core.DataConnectGrpcClient.executeMutation(DataConnectGrpcClient.kt:95)
	at com.google.firebase.dataconnect.core.MutationRefImpl.execute(MutationRefImpl.kt:65)
	at com.google.firebase.dataconnect.QuerySubscriptionIntegrationTest$collect_gets_notified_of_per_data_deserializer_successes$1.invokeSuspend(QuerySubscriptionIntegrationTest.kt:441)
	at com.google.firebase.dataconnect.QuerySubscriptionIntegrationTest$collect_gets_notified_of_per_data_deserializer_successes$1.invoke(Unknown Source:8)
	at com.google.firebase.dataconnect.QuerySubscriptionIntegrationTest$collect_gets_notified_of_per_data_deserializer_successes$1.invoke(Unknown Source:4)

The reason is that the DataConnectAuth object was used before its initialize() method was invoked. PR #6446 changed the logic to invoke initialize() in a separate coroutine, which introduced the race condition. By getting rid of the initialize() method altogether, and simply performing the initialization in an init block in DataConnectAuth (and DataConnectAppCheck) this race condition is completely eliminated.

[github-actions]

📝 PRs merging into main branch

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[github-actions]

Vertex AI Mock Responses Check ⚠️

A newer major version of the mock responses for Vertex AI unit tests is available. update_responses.sh should be updated to clone the latest version of the responses: v5.2

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Test Results

   54 files  ±0     54 suites  ±0   2m 15s ⏱️ +17s
  512 tests  - 3    511 ✅  - 3  1 💤 ±0  0 ❌ ±0 
1 024 runs   - 6  1 022 ✅  - 6  2 💤 ±0  0 ❌ ±0 

Results for commit 93c5daa. ± Comparison against base commit f20340a.

This pull request removes 5 and adds 2 tests. Note that renamed tests count towards both.

com.google.firebase.dataconnect.core.DataConnectAuthUnitTest ‑ close() should succeed if called _after_ initialize()
com.google.firebase.dataconnect.core.DataConnectAuthUnitTest ‑ close() should succeed if called _before_ initialize()
com.google.firebase.dataconnect.core.DataConnectAuthUnitTest ‑ forceRefresh() should throw if invoked before initialize()
com.google.firebase.dataconnect.core.DataConnectAuthUnitTest ‑ getToken() should return re-throw the exception thrown by InternalAuthProvider getAccessToken()
com.google.firebase.dataconnect.core.DataConnectAuthUnitTest ‑ getToken() should throw if invoked before initialize()

com.google.firebase.dataconnect.core.DataConnectAuthUnitTest ‑ close() should succeed if called on a brand new instance()
com.google.firebase.dataconnect.core.DataConnectAuthUnitTest ‑ getToken() should re-throw the exception thrown by InternalAuthProvider getAccessToken()