improvement: generativeaionvertexai_gemini_safety_settings and generativeaionvertexai_gemini_token_count

[gryczj]

Description

Fixes #

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Checklist

• [x] I have followed guidelines from CONTRIBUTING.MD and Samples Style Guide
• [x] Tests pass: npm test (see Testing)
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• [ ] These samples need a new API enabled in testing projects to pass (let us know which ones)
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• [ ] This sample adds a new sample directory, and I updated the CODEOWNERS file with the codeowners for this sample
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[gryczj]

Changes introduced to be consistent with python implementation: https://github.com/GoogleCloudPlatform/python-docs-samples/blob/main/generative_ai/gemini_count_token_example.py and https://github.com/GoogleCloudPlatform/python-docs-samples/blob/main/generative_ai/gemini_safety_config_example.py.

Clarification can be found: https://docs.google.com/document/d/1IwvxzFwLhZIsAUWb48rjzGwnAiWNDQ08pDO6KlLy6ms/edit