Checkbox to auto update link always selected

[PeterNerlich]

Describe the Bug

Our current implementation seems to violate the following paragraph from the original outline in #1878:

When inserting a link, we already have a dialog for selecting an internal content to link to. This dialog needs something like a check box "automatically update link description". This check box should be checked when having no text selected. When having a text selected, the checkbox should be unchecked.

Instead, the checkbox is also checked when text is selected.

Steps to Reproduce

1. Go to any page
2. Select a word that is not yet linked
3. Create a link
4. The Link dialog pops up

Expected Behavior

As existing text is selected, the checkbox should not be checked and the created link should retain it as link text.

Actual Behavior

The checkbox is selected, and if a target is selected and the dialog is submitted in this state, the link retains the originally selected text. However, when submitting the content to the server, the link is immediately updated, as the link text does not reflect the title of the linked page.

Additional Information

To reduce confusion along with fixing the bug, the following changes are proposed:

1. when text is selected, the checkbox should be unchecked
2. when the checkbox is checked on closing the dialog, the link text should be updated right away
3. the checkbox description could be more explicit
4. nice to have: when the checkbox is checked, the text field could be disabled and already show the title of the selected content