Add top_left_arrow cursor symlinks

Summary:
Some mono apps (e.g. KeePass) look for a `top_left_arrow` cursor file instead
of the usual `left_ptr` cursor. Breeze doesn't ship such file, which
means that those mono apps have an ugly mouse cursor on Plasma (see
http://i.imgur.com/D4isxCn.png).

This patch just adds a top_left_arrow -> left_ptr symlink (both for Breeze and
Breeze_Snow).

Test Plan:
`ln -s /usr/share/icons/breeze_cursors/cursors/left_ptr ~/.icons/breeze_cursor/cursors/top_left_arrow`

With such symlink, mono apps use the breeze cursor as expected.

Reviewers: #plasma

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D3459