Sync UI from VertexAI for Firebase

[1998code]

Description of the change

Follow-up from https://github.com/firebase/firebase-ios-sdk/pull/12887

Motivation

Sync the updated User Interface from VertexAI repo.

Type of change

Choose one: Other

Checklist

• [x] I have performed a self-review of my code.
• [x] I have added detailed comments to my code where applicable.
• [x] I have verified that my change does not break existing code.
• [x] My PR is based on the latest changes of the main branch (if unsure, please run git pull --rebase upstream main).
• [x] I am familiar with the Google Style Guide for the language I have coded in.
• [x] I have read through the Contributing Guide and signed the Contributor License Agreement.