Make ClassFieldInner private

Summary:
This shouldn't be public - anyone trying to access it really ought to be
defining helper methods in *this* module, in order to not break up modularity
and make refactors challenging (which is exactly what I've been doing in this
stack - moving use cases that were reaching into the guts into helper methods).

Reviewed By: grievejia

Differential Revision: D70111383

fbshipit-source-id: da96f8978c40f83d774efdc3080e23548261b94a

pyre2/pyre2/lib/alt/class/class_field.rs

@@ -73,10 +73,10 @@ impl ClassFieldInitialization {
 /// know whether it is initialized in the class body in order to determine
 /// both visibility rules and whether method binding should be performed.
 #[derive(Debug, Clone, PartialEq, Eq)]
-pub struct ClassField(pub ClassFieldInner);
+pub struct ClassField(ClassFieldInner);
 
 #[derive(Debug, Clone, PartialEq, Eq)]
-pub enum ClassFieldInner {
+enum ClassFieldInner {
     Simple {
         ty: Type,
         range: Option<TextRange>,