feat: add tests for gemini, fix function calling parameters (#17889)

...s/llama-index-llms-gemini/llama_index/llms/gemini/base.py

...-integrations/llms/llama-index-llms-gemini/pyproject.toml

...ns/llms/llama-index-llms-gemini/tests/test_llms_gemini.py