Notify Content Capture the selection was changed

The ContentCapture service is interested in the selection changes.
When the selection was changed, notifies a text changed event to
ContentCapture.

Bug: 184311217
Test: manual
 1.long press trigger selection, event is sent.
 2.drag selection indicators, send event after the drag is done.
Test: atest CtsContentCaptureServiceTestCases
Change-Id: Ie45f617b132bc240b6cf61ee7ebc3041275f1694