Coerce dictionary types for scalar functions

[viirya]

Describe the bug

Found an issue on coercing dictionary types for scalar function at Comet: apache/datafusion-comet#265

In short, if there are dictionary type and non-dictionary type inputs for scalar function, currently DataFusion cannot coerce the input types, but report an error like:

Error during planning: Coercion from [Dictionary(Int32, Utf8), Utf8] to the signature VariadicEqual failed

To Reproduce

No response

Expected behavior

Dictionary types should be coerced for scalar function.

Additional context

No response