Summary:
Prior to this change various event filters performed deep calls into
Xkb class to figure out the modifiers relevant for global shortcuts (aka
consumed modifiers). This shows that this is a general useful
information which should be available to all input event filters
directly.

Thus it's now added to the input events and exposed directly in
InputRedirection so that the calls into Xkb are no longer needed.

Reviewers: #kwin, #plasma_on_wayland

Subscribers: plasma-devel, kwin

Tags: #plasma_on_wayland, #kwin

Differential Revision: https://phabricator.kde.org/D3810