Accessor properties are faked differently than data properties

When using `leche.fake()`, accessor properties (getters/setters) are set to `undefined` while data properties are created with a getter that throws an error. This was a mistake, as accessor properties should be created the same way as data properties.

Start at the leche.fake() implementation and compare how accessor properties and data properties are created. Make accessor properties follow the same behavior as data properties, then run the existing test suite and confirm both property types no longer produce different results.

Written by the indexing model from the issue text.