message: Expose FrozenHeap from GlobalsBuilder
  Summary: Needed later in the stack, but it is useful API anyway.
diff: @@ -322,6 +322,11 @@ impl GlobalsBuilder {
  )
  }
  + /// Heap where globals are allocated. Can be used to allocate additional values.
  + pub fn frozen_heap(&self) -> &FrozenHeap {
  + &self.heap
  + }
  +
  /// Allocate a value using the same underlying heap as the [`GlobalsBuilder`],
  /// only intended for values that are referred to by those which are passed
  /// to [`set`](GlobalsBuilder::set).
  