Add Firebase AI Logic snippets

[thatfiredev]

This is a tracking issue for snippets being added for the Firebase AI Logic docs:

• Get started
• Generate Text
• Generate Structured output
• Chat - feat(firebase-ai): add Java and Kotlin code snippets #645
• Bidirectional streaming (Live API)
• Analyze Images
• Generate images with Gemini
• Generate images with Imagen
• Analyze video
• Analyze audio
• Analyze PDFs
• Function calling - feat(firebase-ai): add Java and Kotlin code snippets #645
• Grounding - Google Search
• Model configuration - feat(firebase-ai): add Java and Kotlin code snippets #645
• Safety settings - feat(firebase-ai): add Java and Kotlin code snippets #645
• System instructions - feat(firebase-ai): add Java and Kotlin code snippets #645
• Thinking
• Count tokens