To be compatible with the 2024 edition, we need to wrap the
`no_mangle` attribute in `unsafe()`.
The parsing for that in cbindgen was only added in the version 0.28,
but we couldn't upgrade cbindgen before because of a regression in
cbindgen 0.27 that prevented us from upgrading.
Now that cbindgen 0.29 is released with a fix, we can prepare for the
2024 edition
... by changing the resolution for the `WindowItem` to traverse the
item tree from the current item, instead of going to the window.
This doesn't quite fix#4298 because `rem` resolution is still missing.
That requires the built-in default font size function to be fixed as
well, which is non-trivial.
cc #4298
By default it's enabled, of course. This property is not only added to
MenuItem, but Menu as well - since they can be nested. It's also
possible to select a disabled item, but it's hard to modify that since
it's logic is written in Slint. You should be prevented from activating
it with a tap or key press at least.
See #7791
