(cherry-pick) kcms/touchpad: Make sure settings fields in X11 are not randomly missing
Cherry-pick MR for !2730 (merged).
We will now load X11 props early for constants like "supports $xyz".
Before this, if QML makes use of a property during initialization,
it may incorrectly assume "unsupported" for a given libinput feature
and subsequent "load" calls won't fix that value, as its Q_PROPERTY
declaration marks it as CONSTANT.
So let's move anything into the device (LibinputTouchpad) constructor
that determines a Q_PROPERTY without change notifications.
A number of accessors for "supported" flags are simplified because
their .val boolean is sufficient by itself, remaining at their
default false value if the feature is unavailable.
(cherry picked from commit 295b8e61)
Co-authored-by: Jakob Petsovits jpetso@petsovits.com
Edited by Jakob Petsovits