[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