Allow specifying custom dictionary keys for event input.

[L9qmzn]

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Is your feature request related to a problem? Please describe.
When using dictionaries as event inputs in Gradio, we can only use component objects themselves as dictionary keys. This makes it difficult to separate event handling functions from component creation code, as the functions need direct access to the component objects.

Describe the solution you'd like
Allow specifying custom string keys when using dictionaries as event inputs.