[kdiroperator] Allow accessing actions without KActionCollection
KDirOperator provides a set of actions that the using application can access and e.g. add them to their toolbar
Using KActionCollection for this is problematic in several ways:
- The interface is based on internal names, which isn't great
- Exposing a KActionCollection object suggests that this collection can be written to instead of being a read-only view
- It introduces a dependency on KXmlGui, which is something we want to avoid
This patch introduces a new way to obtain the relevant QActions, using enum-based keys for more ergonomic API