> qt: Fix headers
>
> This change is preparation for Qt 6, and it fixes an experimental build
> with Qt 6.2.4.
> qt: Use `|` instead of `+` for key modifiers
>
> This change is preparation for Qt 6 where `+` has been deprecated, and
> it fixes an experimental build with Qt 6.2.4.
> qt: Update deprecated enum value
>
> This change is preparation for Qt 6, and it fixes an experimental build
> with Qt 6.2.4.
> The `Qt::ItemIsTristate` value has been deprecated since 5.6.0 (see
> ae8406d82f541f6d9112bdac192e5e4e114d56aa upstream commit).
This is a backport of core-gui#577
Depends on D18137