[effects/trackmouse] Allow to use both modifiers and shortcut

Summary:
The Track Mouse effect can be toggled either by pressing modifier keys
and moving mouse or by pressing a shortcut. It's not possible to use
the latter and then the former without changing config.

But there is one caveat, in order to use shortcut, you have to uncheck
all modifier keys. This seems to be not very intuitive.

In addition to that, the KCM allows to change shortcut even if there is
some checked modifier.

As the title says, this change makes possible to use both modifier keys
and shortcut to activate this effect without changing config.

KCM:

BUG: 398124
FIXED-IN: 5.14.0

Reviewers: KWin, Plasma, VDG, davidedmundson

Reviewed By: KWin, Plasma, VDG, davidedmundson

Subscribers: broulik, abetts, ngraham, kwin

Tags: KWin

Differential Revision: https://phabricator.kde.org/D15272