Update vertexai changelog file

[rlazo]

It includes the full list of changes since the last release.

[github-actions]

Release note changes

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

Release Notes

firebase-vertexai

### {{firebase_vertexai}} version 16.0.0 {: #vertex-ai_v16-0-0}

* {{feature}} Added support for `title` and `publicationDate` in citations. GitHub [#6309](//github.com/firebase/firebase-android-sdk/issues/6309){: .external}

* {{feature}} Added support for `frequencyPenalty`, `presencePenalty`, and `HarmBlockMethod`. GitHub [#6309](//github.com/firebase/firebase-android-sdk/issues/6309){: .external}

* {{changed}} **Breaking Change**: Introduced `Citations` class. Now `CitationMetadata` wraps that type. GitHub [#6276](//github.com/firebase/firebase-android-sdk/issues/6276){: .external}

* {{changed}} **Breaking Change**: Introduced `FunctionCall` and `FunctionResponse` types. Now `FunctionCallPart` and `FunctionResponsePart` wrap those types, respectively. GitHub [#6311](//github.com/firebase/firebase-android-sdk/issues/6311){: .external}

* {{changed}} **Breaking Change**: Reworked `Schema` declaration mechanism. GitHub [#6258](//github.com/firebase/firebase-android-sdk/issues/6258){: .external}

* {{changed}} **Breaking Change**: Reworked function calling mechanism to use the new `Schema` format. Function calls no longer use native types, nor include references to the actual executable code. GitHub [#6258](//github.com/firebase/firebase-android-sdk/issues/6258){: .external}

* {{changed}} **Breaking Change**: Made `totalBillableCharacters` field in `CountTokens` nullable and optional. GitHub [#6294](//github.com/firebase/firebase-android-sdk/issues/6294){: .external}

* {{changed}} **Breaking Change**: Removed `UNKNOWN` option for the `HarmBlockThreshold` enum. GitHub [#6294](//github.com/firebase/firebase-android-sdk/issues/6294){: .external}

* {{changed}} **Breaking Change**: Removed `UNSPECIFIED` option for the `HarmBlockThreshold`, `HarmProbability`, `HarmSeverity`, and `BlockReason` enums. GitHub [#6294](//github.com/firebase/firebase-android-sdk/issues/6294){: .external}

* {{changed}} **Breaking Change**: Renamed `BlockThreshold` as `HarmBlockThreshold`. GitHub [#6262](//github.com/firebase/firebase-android-sdk/issues/6262){: .external}

* {{changed}} **Breaking Change**: Renamed all types and methods starting with `blob` to start with `inlineData`. GitHub [#6309](//github.com/firebase/firebase-android-sdk/issues/6309){: .external}

* {{changed}} **Breaking Change**: Changed the order of arguments in `InlineDataPart` to match `ImagePart`. GitHub [#6340](//github.com/firebase/firebase-android-sdk/issues/6340){: .external}

* {{changed}} **Breaking Change**: Changed `RequestOption` to accept only `long` timeout values. GitHub [#6289](//github.com/firebase/firebase-android-sdk/issues/6289){: .external}

* {{changed}} **Breaking Change**: Moved `requestOptions` to the last positional argument in the `generativeModel` argument list. GitHub [#6292](//github.com/firebase/firebase-android-sdk/issues/6292){: .external}

* {{changed}} **Breaking Change**: Replaced sealed classes with abstract classes for `StringFormat`. GitHub [#6334](//github.com/firebase/firebase-android-sdk/issues/6334){: .external}

* {{changed}} **Breaking Change**: Refactored enum classes to be normal classes. GitHub [#6340](//github.com/firebase/firebase-android-sdk/issues/6340){: .external}

* {{changed}} **Breaking Change**: Marked `GenerativeModel` properties as private. GitHub [#6309](//github.com/firebase/firebase-android-sdk/issues/6309){: .external}

[daymxn]

+1, but I defer to @rachelsaunders for final approval

[github-actions]

Test Results

 20 files  ±0   20 suites  ±0   14s ⏱️ -1s
112 tests ±0  112 ✅ ±0  0 💤 ±0  0 ❌ ±0 
224 runs  ±0  224 ✅ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit fedf744. ± Comparison against base commit b1da895.

♻️ This comment has been updated with latest results.