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ARROW-9751: [Rust] [DataFusion] Allow UDFs to accept multiple data types per argument

This PR aligns UDFs registration and declaration to be consistent with our built-in functions, so that we can leverage coercion rules on their arguments.

For ease of use, this PR introduces a function `create_udf` that simplifies the creation of UDFs with a fixed signature and fixed return type, so that users have a simple interface to declare them.

However, underneath, the UDFs have the same capabilities as built-in functions, in that they can be as generic as built-in functions (arbitrary types, etc.).

Specific achievements of this PR:

* Added example (120 LOC) of how to declare and register a UDF
* Deprecated the type coercer optimizer, since it was causing logical schemas to become misaligned and cause our end-to-end tests to faail when implicit casting was required, and replaced it by what we already do for built-ins
* Made UDFs use the same interfaces as built-in functions

Note that this PR is built on top of #8032.

Closes #7967 from jorgecarleitao/clean

Authored-by: Jorge C. Leitao <jorgecarleitao@gmail.com>
Signed-off-by: Andy Grove <andygrove73@gmail.com>