Rename / simplify BuiltInWindowExpr / BuiltInWindowFunctionExpr

[alamb]

Is your feature request related to a problem or challenge?

• We have completed converting all window functions to use the user defined API (specifically WindowFunctionImpl). See [Epic] Unify WindowFunction Interface (remove built in list of BuiltInWindowFunction s) #8709

However, there are still a few structures named BuiltInWindow* that now no longer reflect the reality that there are no more "built in" functions:

A BuiltInWindowExpr here:

datafusion/datafusion/physical-expr/src/window/built_in.rs

Lines 38 to 45 in 22c1f54

	/// A window expr that takes the form of a [`BuiltInWindowFunctionExpr`].
	#[derive(Debug)]
	pub struct BuiltInWindowExpr {
	expr: Arc<dyn BuiltInWindowFunctionExpr>,
	partition_by: Vec<Arc<dyn PhysicalExpr>>,
	order_by: LexOrdering,
	window_frame: Arc<WindowFrame>,
	}

A BuiltInWindowFunctionExpr:

datafusion/datafusion/physical-expr/src/window/built_in_window_function_expr.rs

Lines 30 to 39 in 22c1f54

	/// Evaluates a window function by instantiating a
	/// `[PartitionEvaluator]` for calculating the function's output in
	/// that partition.
	///
	/// Note that unlike aggregation based window functions, some window
	/// functions such as `rank` ignore the values in the window frame,
	/// but others such as `first_value`, `last_value`, and
	/// `nth_value` need the value.
	#[allow(rustdoc::private_intra_doc_links)]
	pub trait BuiltInWindowFunctionExpr: Send + Sync + std::fmt::Debug {

Which confusingly is implemented for WindowUDFExpr:

datafusion/datafusion/physical-plan/src/windows/mod.rs

Lines 218 to 221 in d840e98

	impl BuiltInWindowFunctionExpr for WindowUDFExpr {
	fn as_any(&self) -> &dyn std::any::Any {
	self
	}

Describe the solution you'd like

1. I would like to rename the confusing BuiltIn prefix for these structures
2. Leave backwards compatibility typedefs type BuiltInWindowExpr = ... to ease migration

Describe alternatives you've considered

I would recommend first simply renaming the structs / traits to remove the BuiltIn prefix / module names

Then I also think it is worth seeing if the BuiltInWindowFunctionExpr trait is still needed, or if the code in physical plan could simply call WindowUDF directly

Additional context

No response

[irenjj]

take