IE 11 no longer supports the legacy document.selection API.
Their implementation of window.getSelection() doesn't support
the extend() method, which we were relying on.
If the selection is RTL and selection extend is missing, then just
flip the selection.
Polyfill 'onSelect' behavior for React.
Use non-standard 'selectionchange' event rather than 'select' event.
This allows us to fire the event when user moves the cursor via arrow
keys, and not just when they select multiple chars.
Add methods to ReactDOMSelection to make getting current selection
easier, so we can do a fast check for change without having to
calculate char offsets for selection start and end.
Add a DOM based selection module. This can both be used on its own and
in ReactInputSelection where our current implementation is lacking.
There is still some inconsistency with how IE and modern browsers
handle block nodes. Should be OK if we are just getting and setting
and not trying to set selection based on character offsets.
