[AI] Add converter functions to translate mlkit and interop

[rlazo]

To make it easier to work between both type sets, the converters group together the code necessary for communication between SDKs in a single point.

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[rlazo]

/gemini review

[google-oss-bot]

	1 Warning
⚠️	Did you forget to add a changelog entry? (Add the 'no-changelog' label to the PR to silence this warning.)

Generated by 🚫 Danger

[gemini-code-assist]

Code Review

This pull request introduces a new file with converter functions to translate between ML Kit and interop data types. The implementation is mostly straightforward, but I've found a significant bug where the image part of a request is ignored during conversion. I've provided a suggestion to fix this. I also included a minor suggestion to make the code more idiomatic and concise. Overall, good work on centralizing the conversion logic.

[rlazo]

The code in this PR depends on #7663 landing, so it won't build before that PR lands.