Use contextually-appropriate icon for GlobalDrawer handle button

Summary:
Now that the GlobalDrawer's icon can be customized (see D23154), let's use a more
contextually-appropriate icon for Kamoso's GlobalDrawer, which has the effects in it

Test Plan: {F7247606, size=full}

Reviewers: #vdg, apol

Reviewed By: apol

Differential Revision: https://phabricator.kde.org/D23160