Implement FromMeta for syn::ExprPath

[FlixCoder]

Hi!

Darling allows this nicely:

[derive(Debug, FromField)]
#[darling(attributes(merge))]
struct FieldAttrs {
	#[darling(default)]
	pub custom: Option<syn::Path>,
}

But the same is not possible with ExprPath, as FromMeta is not implemented for it:

[derive(Debug, FromField)]
#[darling(attributes(merge))]
struct FieldAttrs {
	#[darling(default)]
	pub custom: Option<syn::ExprPath>,
}

the trait bound `syn::ExprPath: darling::FromMeta` is not satisfied
required because of the requirements on the impl of `darling::FromMeta` for `std::option::Option<syn::ExprPath>`

Use case: e.g. serde uses ExprPath to specify a function to apply to fields in certain actions (serialize_with). I would like to do something similar. syn::Path does not allow to use generics inside the path.

Is there another way to solve this? Can FromMeta be implemented for it?