Replace directories-next dependency with directories (#4661)

`directories-next` was created because `directories` was not maintained
at the time. However, `directories` has gotten active maintainership
since, and it has received more updates than `directories-next`.

`directories` also has more recent downloads than its `next`
counterpart, so it might make sense to switch to it, to avoid
unnecessary duplicate dependencies, where a project depends transitively
on both `directories` and `directories-next`.

The main question is whether we depend on any specific behavior from
`directories-next`.

crates/eframe/Cargo.toml

@@ -70,7 +70,7 @@ glow = [
 
 ## Enable saving app state to disk.
 persistence = [
-  "directories-next",
+  "directories",
   "egui-winit/serde",
   "egui/persistence",
   "ron",
@@ -159,7 +159,7 @@ image = { workspace = true, features = ["png"] } # Needed for app icon
 winit = { workspace = true, default-features = false, features = ["rwh_06"] }
 
 # optional native:
-directories-next = { version = "2", optional = true }
+directories = { version = "5", optional = true }
 egui-wgpu = { workspace = true, optional = true, features = [
   "winit",
 ] } # if wgpu is used, use it with winit