[DRAFT] Update AI Toolkit docs

[csells]

Updates to the AI Toolkit for firebase_ai updates and updates pending for a future release.

Presubmit checklist

• If you are unwilling, or unable, to sign the CLA, even for a tiny, one-word PR, please file an issue instead of a PR.
• If this PR is not meant to land until a future stable release, mark it as draft with an explanation.
• This PR follows the Google Developer Documentation Style Guidelines—for example, it doesn't use i.e. or e.g., and it avoids I and we (first-person pronouns).
• This PR uses semantic line breaks
  of 80 characters or fewer.

[csells]

fyi @sfshaza2

[flutter-website-bot]

Visit the preview URL for this PR (updated for commit 6488fb4):

https://flutter-docs-prod--pr12751-ai-toolkit-update-72sjduwl.web.app

[marb2000]

Use Firebase AI Logic as product name, and not Vertex AI for Firebase.