Add a new ChatGoogleGenerativeAI class in a `langchain-google-genai`
package.
Still todo: add a deprecation warning in PALM
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Co-authored-by: Erick Friis <erick@langchain.dev>
Co-authored-by: Leonid Kuligin <lkuligin@yandex.ru>
Co-authored-by: Bagatur <baskaryan@gmail.com>
