Deprecate Dict::new

Summary:
* We may want to have more efficient dict representation on the heap, for example, store dict data in starlark heap rather than malloc, this is how list is implemented
* This code is function is not as useful when typechecking and documentation is important: if we allocate the dict explicitly, and pass it to `heap.alloc()`, we no longer can use it as function return value

Reviewed By: shonaganuma

Differential Revision: D50484424

fbshipit-source-id: 2514b537c0a3790c8ec812971e11c479348975fc

starlark/src/values/types/dict/value.rs

@@ -195,7 +195,9 @@ impl<'v> Dict<'v> {
         DictGen::<FrozenDictData>::get_type_value_static()
     }
 
-    /// Create a new [`Dict`].
+    /// This function is deprecated.
+    /// Use [`AllocDict`](crate::values::dict::AllocDict) or [`SmallMap`]
+    /// to allocate a new dictionary on the heap.
     pub fn new(content: SmallMap<Value<'v>, Value<'v>>) -> Self {
         Self { content }
     }