fix: locale selector + autosave race condition (#7891)

## Description

Fixes a race condition where you could switch locales and have autosave
trigger with old locale data.

By adding the `key` to the `Document` component, we will ensure that the
entire `Document` will be un-mounted and re-mounted between locale
switches.

packages/next/src/views/Document/index.tsx

@@ -280,6 +280,7 @@ export const Document: React.FC<AdminViewProps> = async ({
       initialData={data}
       initialState={formState}
       isEditing={isEditing}
+      key={locale?.code}
     >
       {!RootViewOverride && (
         <DocumentHeader