[ci skip] Fix documentation in PropertyAccessors
[ci skip] Fix documentation in PropertyAccessors

Function to enable accessors is `_enableProperties`, and should be
called in the `connectedCallback`

JeremybellEU/polymer,JeremybellEU/polymer,Polymer/polymer,JeremybellEU/polymer,ikeagold/polymer,ikeagold/polymer,ikeagold/polymer,Polymer/polymer,Polymer/polymer