libs.versions.toml: add ThreeTenAbp (backport of java.time for Android)

[dconeybe]

Add "ThreeTenAbp" to libs.versions.toml. This library is a backport of the new JDK8 date and time classes in java.time to JDK7. Although we should definitely NOT use this library in production, it's quite useful in unit and integration tests to perform complicated date and time mathematics. Once the minSdkVersion is changed to 26 or later, we can drop this dependency and simply use the java.time classes from the standard library.

Although this PR does not contain any actual uses of the library, a follow-up PR will use it, and I wanted to separate the global change of modifying libs.versions.toml from the test code that makes use of it because changing libs.versions.toml has a project-wide blast radius.

For details, see https://www.threeten.org/threetenbp/ and https://github.com/JakeWharton/ThreeTenABP, the latter being the Android-specific backport added to libs.versions.toml by this PR.

[github-actions]

Release note changes

No release note changes were detected. If you made changes that should be
present in the next release, ensure you've added an entry in the appropriate
CHANGELOG.md file(s).

[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.

[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: v5.1

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Test Results

 1 022 files  ±0   1 022 suites  ±0   35m 40s ⏱️ -58s
 5 809 tests ±0   5 787 ✅ ±0  22 💤 ±0  0 ❌ ±0 
11 703 runs  ±0  11 659 ✅ ±0  44 💤 ±0  0 ❌ ±0 

Results for commit 76087bf. ± Comparison against base commit 0697dd3.

♻️ This comment has been updated with latest results.