Add a "Reload" menu item to KDirOperator's context menu

Summary:
Add a {nav Reload} menu item to `KDirOperator`'s context menu, so clients that don't display a toolbar but might need to refresh views manually (such as Kate's Filesystem Browser view} can do it.

BUG: 199994
FIXED-IN: 5.46

Test Plan:
Enable Kate's Filesystem Browser plugin and right-click in it:
{F5808015}

It also appears in more common `KDirOperator` clients, such as the open/save dialogs:
{F5808016}

Reviewers: #frameworks, hein

Reviewed By: hein

Subscribers: maximilianocuria, dhaumann, rkflx

Tags: #frameworks

Maniphest Tasks: T8552

Differential Revision: https://phabricator.kde.org/D12215