Maintain selection on update in code and text mode

[josdejong]

Since version v5.20.0, JSONEditor contains new methods update and updateText which keep the current state of the editor when in modes tree, form, and view. These methods work for text and code too, but there the caret position is lost when updating the contents of the editor.

It would be great if the caret position could be maintained too. Ace editor has support for updating with a text diff, that will be really useful. I think we'll need a text diff library to determine which parts are changed, so we can calculate how much the old selection needs to move up or down to match the same contents.