Option to `Select assigned media` is incorrectly available for linked processes

[solth]

Describe the bug In #6683 a new option was added to the context menu of tree nodes in the logical structure tree of the metadata editor, to select all media assigned to a selected logical structure element. This option is incorrectly also available for media entries (like pages) and for links to other processes.

To Reproduce Steps to reproduce the behavior:

1. Open a process with media or links to other processes in the metadata editor
2. Right click on the media or linked process in the logical structure tree to open its context menu
3. See the wrong menu option to "Select assigned media"

Expected behavior The option to select assigned media should only be available in the context menu of logical structure elements, not in the context menu of linked processes or views/media.

Screenshots

Release current main branch