[VLM] Implement merged multimodal processor for Mllama

[Isotr0py]

• Initialize merged multimodal processor implementation for encoder-decoder LMMs

[github-actions]

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[DarkLight1337]

To avoid scope creep, let's wait until #11396 has been merged first.

[DarkLight1337]

For that PR, I'm waiting for @ywang96 to perform benchmarks to confirm the effectiveness of the cache.

[Isotr0py]

No problem, there is no rush for this PR. :)