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:

https://github.com/apache/datafusion/blob/98cd19ef1cf52aef647e3e43fcc132a93028d1a2/datafusion/functions-aggregate/src/first_last.rs#L75

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.