[FIX] web_editor: save a historyStep upon cut

Before this commit, _onClipboardCut removed the selected text but did not
register it as a history step. Other than not storing history properly,
this caused unexpected behavior when followed by an action that leads to a
historyRollback on the current step, such as those in _onInput.

task-3142995

closes odoo/odoo#110453

Signed-off-by: David Monjoie (dmo) <dmo@odoo.com>