Send TYPE_VIEW_TEXT_CHANGED a11y event when SuggestionSpan is added

When user types space after a word, we receive a text
change event, but the suggestion span is not added to
the text yet. The spell checker adds the span after the
text change event is sent, but currently TextView doesn't send
any notification. This change sends a TYPE_VIEW_TEXT_CHANGED
event with the from and to index of the span, and beforeText
which doesn't have the span and afterText which has the
span.

Bug: b/143378480

Test: tested with talkback.

Change-Id: If16c2c578be5dcae20a9fd7014ff6fba2d487670