[Application Dashboard] Improve mouse handler
Summary:
- Do not close Application Dashboard after dragging items
- Correct the view attached property to GridView.view
BUG: 390424
Test Plan: - Application Dashboard is not closed when dragging items in the Favorites column.
Reviewers: hein, ngraham, Plasma
Reviewed By: hein, ngraham, Plasma
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D19800