Implementation of a popup button to rotate the screen while using gesture navigation.
The button is set to appear when the device rotates while auto rotation is off. Then the button will be visible for a short period of time before disappearing.
This is partially an emergency fix also for
https://invent.kde.org/plasma/plasma-mobile/-/issues/404, which was
potentially introduced by https://invent.kde.org/plasma/plasma-mobile/-/merge_requests/582
This MR extracts the screen brightness implementation from initialstart
to a QML plugin, and also ports the action drawer brightness slider
implementation to it. This avoids importing the powerdevil screen
brightness plugin on the lockscreen, which apparently has a race
condition that causes it to sometimes segfault.
This allows us in the future to use mobileshell without having the WindowUtil singleton loaded (which does a bunch of wayland calls that aren't necessary for most applications).
Move from a C++ library + QML plugin to a QML plugin only for simplicity, since the homescreen switching architecture will be done from Plasma, and so use of the shell library only needs to be from QML.
