Use lowercase name for aggregate function

[alamb]

Is your feature request related to a problem or challenge?

first_value and last_value window functions currently report their names as FIRST_VALUE but also have a lower case alias:

datafusion/datafusion/functions-aggregate/src/first_last.rs

Line 75 in 98cd19e

aliases: vec![String::from("first_value")],

part of #8708

Describe the solution you'd like

I think we would like to avoid the aliases and simply have a single name, similarly how the other functions work

TODO

• Count

Describe alternatives you've considered

No response

Additional context

No response

[jayzhan211]

I think we need to rename other builtin aggregate function to lowercase too.

[edmondop]

This might be solved too? @alamb

[jayzhan211]

Yeah, solved