message: wasm_engine: clarify behaviour of get_memory/set_memory
diff: @@ -33,11 +33,15 @@ public:
  /// Requires parse().
  virtual void instantiate() = 0;
  - /// Returns the memory of the internal instance.
  + /// Returns the entire memory of the internal instance.
  + /// It must return memory index 0 and the size must be a multiple of the page size.
  + /// Can return an empty view if no memory is available (exported).
  /// Requires instantiate().
  virtual bytes_view get_memory() const = 0;
  /// Replaces the memory of the internal instance with the provided one.
  + /// It must change memory index 0.
  + /// Should not fail if the input is empty (no update) and there is no memory available.
  /// Requires instantiate().
  virtual void set_memory(bytes_view memory) = 0;
  