LogicalPlan Casts can't express a cast to an extension type

[paleolimbot]

Is your feature request related to a problem or challenge?

The current Expr::Cast can't represent a cast to an extension type because it uses DataType as the target:

datafusion/datafusion/expr/src/expr.rs

Lines 1009 to 1016 in 77ec319

	/// Cast expression
	#[derive(Clone, PartialEq, Eq, PartialOrd, Hash, Debug)]
	pub struct Cast {
	/// The expression being cast
	pub expr: Box<Expr>,
	/// The `DataType` the expression will yield
	pub data_type: DataType,
	}

I noticed this in #17986 because a FieldRef is a way to support extension types like UUID in SQL but this information will get dropped when constructing the logical plan.

(I'd personally love this so that we can support casting to GEOMETRY/GEOGRAPHY in SedonaDB)

Describe the solution you'd like

Update the internal representation of the Cast to use a FieldRef or add an Option<FieldMetadata> to it so that it can express the operation of casting to an arbitrary type.

Describe alternatives you've considered

No response

Additional context

No response

[Weijun-H]

I don’t mind changing the DataType to FieldRef here since it would support a wider range of types. However, it could be a major api change, so I’ll wait for other opinions before proceeding.

If needed, I can take on this issue.

[paleolimbot]

I don't mind either way...I think a FieldRef will make it less likely that will accidentally drop metadata (which is very difficult to track down), at the expense of potentially breaking existing pub field access. This would also let a cast express nullability which may be helpful if it can be respected (is there another way to make a nullable field nullable or vice versa?).

After I finish with the Placeholder update I'm happy to take a look at this (or feel free to start and I can review!)