dataconnect: DateSerializer removed, as it is superceded by LocalDateSerializer

[dconeybe]

As of Data Connect emulator version 1.7.0, the generated Kotlin code uses com.google.firebase.dataconnect.LocalDate instead of java.util.Date. Therefore, DateSerializer is no longer needed and is deleted by this PR.

This is a breaking change. If generated code depends on DateSerializer simply upgrade the Data Connect emulator to generate code that uses LocalDate instead of java.util.Date.

[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

[github-actions]

Test Results

   58 files  ±0     58 suites  ±0   2m 1s ⏱️ -3s
  535 tests ±0    534 ✅ ±0  1 💤 ±0  0 ❌ ±0 
1 070 runs  ±0  1 068 ✅ ±0  2 💤 ±0  0 ❌ ±0 

Results for commit c2c9273. ± Comparison against base commit a6afee2.

[github-actions]

Test Results

   58 files  ±0     58 suites  ±0   2m 2s ⏱️ -9s
  535 tests ±0    534 ✅ ±0  1 💤 ±0  0 ❌ ±0 
1 070 runs  ±0  1 068 ✅ ±0  2 💤 ±0  0 ❌ ±0 

Results for commit d7976eb. ± Comparison against base commit b61a095.

♻️ This comment has been updated with latest results.

[github-actions]

Release note changes

The following release notes were modified. Please ensure they look correct.

Release Notes

firebase-dataconnect

### {{data_connect_short}} version 16.0.0-beta03 {: #data-connect_v16-0-0-beta03}

* {{changed}} Requires Data Connect emulator version 1.6.1 or later for code generation.

* {{feature}} QueryRef and MutationRef gain methods copy(), withDataDeserializer(),
  and withVariablesSerializer().
  (GitHub [#6424](//github.com/firebase/firebase-android-sdk/issues/6424){: .external})

* {{feature}} GeneratedConnector gains methods copy(), operations(), queries(),
  and mutations().
  (GitHub [#6424](//github.com/firebase/firebase-android-sdk/issues/6424){: .external})

* {{feature}} GeneratedQuery and GeneratedMutation gain methods copy(),
  withVariablesSerializer(), and withDataDeserializer().
  (GitHub [#6424](//github.com/firebase/firebase-android-sdk/issues/6424){: .external})

* {{feature}} GeneratedConnector, GeneratedQuery, and GeneratedMutation now
  must implement equals() to be a _logical_ comparsion, rather than just
  checking for _referencial_ equality using the `===` operator.
  (GitHub [#6424](//github.com/firebase/firebase-android-sdk/issues/6424){: .external})

* {{feature}} ExperimentalFirebaseDataConnect annotation added, and some
  APIs have been annotated with it, requiring applications that make use of
  these experimental APIs to opt-in using
  `@OptIn(ExperimentalFirebaseDataConnect::class)` to suppress warnings or
  errors related to using these experimental APIs.
  (GitHub [#6424](//github.com/firebase/firebase-android-sdk/issues/6424){: .external}) and
  (GitHub [#6433](//github.com/firebase/firebase-android-sdk/issues/6433){: .external})

* {{changed}} Replaced java.util.Date with
  com.google.firebase.dataconnect.LocalDate.
  (GitHub [#6434](//github.com/firebase/firebase-android-sdk/issues/6434){: .external})

* {{changed}} `DateSerializer` removed, as it is superceded by
  `LocalDateSerializer`. As of Data Connect emulator version 1.7.0, the
  generated Kotlin code uses `com.google.firebase.dataconnect.LocalDate`
  instead of `java.util.Date`. Therefore, this version of the SDK must be
  paired with code generated by version 1.7.0 (or later) of the Data Connect
  emulator.
  (GitHub [#6513](//github.com/firebase/firebase-android-sdk/issues/6513){: .external})

[github-actions]

📝 PRs merging into main branch

Our main branch should always be in a releasable state. If you are working on a larger change, or if you don't want this change to see the light of the day just yet, consider using a feature branch first, and only merge into the main branch when the code complete and ready to be released.