Implement read-only/view mode for contact details view

[dschrempf]

Is your feature request related to a problem? Please describe.

When opening the contacts on Nextcloud, I am always afraid that I add or delete characters or other things to the fields by accident.

Describe the solution you'd like

• When viewing a contact, the contact should be in "read-only" (or "viewing") mode by default.
• There should be a button "Edit" to edit the contact
• The "Save" button should be in the same place as the "Edit" button after toggling modes.
• [Contact Details] Show quick actions in view mode #3352
• Switch between view and edit mode should not cause jumping around of text. The text is placed such that on changing to edit mode, the position of the text itself changes as little as possible, and only a border appears around the text indicating an input field.
• Switching between view and edit mode should not change the position of the Edit/save button either, esp. in mobile view.

Mockups are at #3305.

Describe alternatives you've considered

None

Additional context

Thanks for considering this feature request!

[ChristophWurst]

This is mentioned in #2699 too

[st3iny]

I added more bullet points from #1923 (comment).

[ChristophWurst]

Let's also move and merge the todos and screenshots from #1923 (comment) into this ticket for better clarity.

[dschrempf]

Thank you so much for your work on this!