[Model] Use merge_by_field_config for MM models (H-L)

[DarkLight1337]

Purpose

Part of #26149

Test Plan

Tested all models other than Kimi-VL (doesn't work with latest Transformers)

Test Result

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• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
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[gemini-code-assist]

Code Review

This pull request refactors several multi-modal models (Idefics3, Keye, Keye-VL 1.5, Kimi-VL) to use a new centralized mechanism for handling multi-modal inputs, enabled by the merge_by_field_config flag. This is a good maintainability improvement as it removes duplicated validation and reshaping code from individual model files. However, I've found a couple of potential issues. For Kimi-VL, specific reshaping logic has been removed, which is likely to break the model since it could not be tested. For Idefics3, enabling merge_by_field_config will use an existing configuration function that appears to be incorrect for image_embeds and num_patches. I've left detailed comments on these issues. The changes for other models and the improvements to error messages in tensor_schema.py are positive.

[DarkLight1337]

cc @Isotr0py