Reuse effective substatements along entire copy axis

In the following model:

module foo {
  namespace foo;
  prefix foo;

  grouping grp {
    container foo;
  }

  container bar {
    uses grp;
  }

  container baz {
    uses grp;
  }
}

We end up with distinct objects for bar/foo and baz/foo. Disregarding SchemaPath, this is because the effectiveConfig property changes separately and the instantiation of baz/foo does not see the object at bar/foo (and vice-versa).

In order to make this work we need to instantiate a statement-specific lookup table in grp/foo's ReactorStmtCtx. When instantiating bar/foo, this would be populated with an effective key, i.e. effectiveConfig + history (+ whatever) and pointing to bar/foo. When instantiating baz/foo, the bar/foo instance would be recognized as the equivalent and reused.