An observer interface for pivot changes.
Called when the pivot changes.
| aPivot | [in] the pivot that has changed. |
| aOldAccessible | [in] the old pivot position before the change, or null. |
| aOldStart | [in] the old start offset, or -1. |
| aOldEnd | [in] the old end offset, or -1. |
| aReason | [in] the reason for the pivot change. |
| aIsFromUserInput | [in] the pivot changed because of direct user input (default is true). |