feature: implement flutter's TextSelection class

[DarkWolf260]

Flet should have events for text selection or be able to call an event that interacts with the selected text.

Useful for any case that requires manipulating a text selection.

Use Case: how to make a text editor with functions like bold, underline or italic.

plz :'(

Link to Flutter: https://api.flutter.dev/flutter/services/TextSelection-class.html

[yunguangli]

I second this.