[applets/taskmanager] Clean up Tooltip code
Summary:
The ToolTip code was kind of messy. This patch adjusts it to use modern Layouts,
fixes some binding loops, reduces redundancy, adds comments, removes a lot of
unnecessary code, and ports almost everything to PlasmaComponents3. We still
need PC2 for Highlight so it can't be removed entirely.
There is only one unavoidable visual change, which was made in this patch
because it is consistent with the latest VDG mockup (T12640): the blurred
album art background no longer goes under the player controls bar. This
simplifies the code substantially, and as the mockup shows, it just looks better
anyway (IMO).
This is not intended to fully implement the mockup in T12640.
Test Plan:
Everything looks the same, except for this:
Reviewers: Plasma, VDG, ndavis
Reviewed By: VDG, ndavis
Subscribers: hein, trmdi, broulik, plasma-devel
Tags: Plasma
Maniphest Tasks: T12640
Differential Revision: https://phabricator.kde.org/D27182