feat(firebaseai): add responseJsonSchema to GenerationConfig

[gspencergoog]

Description

This adds the responseJsonSchema field to the GenerationConfig class, which enables more JSON schema features like $def and $ref along with other advanced JSON schema features that Gemini 2.5 supports.

See the Gemini docs for more information about what is supported.

Related Issues

• Fixes 🚀 [firebase_ai] Support for advanced Schema features with $ref and $def #17551

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[rodydavis]

LGTM

[cynthiajoan]

Thanks for the PR, would like to check if it has been tested under both vertexAI and googleAI backend.

[gspencergoog]

Thanks for the PR, would like to check if it has been tested under both vertexAI and googleAI backend.

Yes, I've tested it on both backends.

[gspencergoog]

Okay, @cynthiajoan I added an example here that uses $def and $anchor, which wasn't possible before this change.

I also formatted the output a little better in the "chat" of the example, and updated the regular schema example to match.

I also bumped the Gemini model versions in the example's main, since they were pretty old, but I'm happy to revert that if you wanted them to stay that way.