LineEdit/TextEdit: Add Shift+Delete shortcut for cut
Closes #4060 (closed)
This PR was only supposed to add this shortcut, but I found some inconsistencies with the copy, cut and paste code in TextEdit, which produced weird results when combining shortcuts and menu actions (e.x.: cutting with Ctrl+X and pasting with Edit -> Paste).
Now both the shortcuts and the menu actions use the same code.
Let me know if you prefer this to go into a separate PR.