* Add an additional flag moveCursor to OpInsertText,
and obey it to explicitly move the cursor to the
desired resultant position.
When doing this, take care to specify the correct
textnode position for text insertion (i.e. before
or after the cursor).
* Adapt the rest of the code that uses OpInsertText
to pass the correct moveCursor flag (true).
* Remove the 'return null' from the transform of
InsertText vs InsertText.
Adapt tests to specify the moveCursor flag
when using OpInsertText.