message: Replace complicated type with type alias
  The same as in sys/store.rs
diff: use std::fmt;
  use wasmer_types::OnCalledAction;
  +/// Call handler for a store.
  +// TODO: better documentation!
  +// TODO: this type is duplicated in sys/store.rs.
  +// Maybe want to move it to wasmer_types...
  +pub type OnCalledHandler = Box<
  + dyn FnOnce(StoreMut<'_>) -> Result<OnCalledAction, Box<dyn std::error::Error + Send + Sync>>,
  +>;
  +
  /// We require the context to have a fixed memory address for its lifetime since
  /// various bits of the VM have raw pointers that point back to it. Hence we
  /// wrap the actual context in a box.
  pub(crate) struct StoreInner {
  pub(crate) objects: StoreObjects,
  - pub(crate) on_called: Option<
  - Box<
  - dyn FnOnce(
  - StoreMut,
  - )
  - -> Result<OnCalledAction, Box<dyn std::error::Error + Send + Sync>>,
  - >,
  - >,
  + pub(crate) on_called: Option<OnCalledHandler>,
  }
  /// The store represents all global state that can be manipulated by
  