This change adds `KeyPress` and `KeyRelease` variants to the `WindowEvent` enum, along with the new `slint::Key` enum, that allows encoding keys.
Now it's also possible to toggle checked by click on the text of the CheckBox similar to fluent design GroupBox now respect the minimum width of the title, to avoid elision Adopt SpinBox: set focus when buttons are clicked #1795 on md SpinBox
Add material, material-light and material-dark widgets and make it available by the `env` `SLINT_STYLE`.
