Added support for responses that include both text and functionCall parts (or other content types in the future).
Note: Multiple text parts in a single response is theoretical at this time (may need to revisit the joining approach if the output doesn't match our expectations).
Also added a test for parallel function calling (multiple functionCall parts in one response).
textandfunctionCallparts (or other content types in the future).textparts in a single response is theoretical at this time (may need to revisit the joining approach if the output doesn't match our expectations).functionCallparts in one response).See https://github.com/firebase/firebase-js-sdk/pull/8229 for JS (Vertex AI) equivalent.