feat: Add slot for description of NcEmptyContent

[susnux]

• Follow up on enh(NcEmptyContent): allow customizing the title #3791

Like the title this allows to override the default behavior of the description by providing a slot for it.
This way you could pass in formatted content (e.g. using emphasis / strong emphasis ...).

Note: Maybe move the slot inside the paragraph element?

[raimund-schluessler]

Fine with me, although I am a bit skeptical whether we should allow this much adjustments, or rather keep it consistent.

[susnux]

I know what you mean, maybe we should move the slot inside the <p> to restrict the content to inline elements.

And maybe the title should (have been) restricted to a prop accepting only h elements for different heading levels but no custom elements?

[raimund-schluessler]

I know what you mean, maybe we should move the slot inside the <p> to restrict the content to inline elements.

And maybe the title should (have been) restricted to a prop accepting only h elements for different heading levels but no custom elements?

I think this would be to much coding effort to restrict it. Maybe we simply give a hint in the description of the slot.

[max-nextcloud]

Ok with me if there's a need for this.

[susnux]

Rebased this and added the discussed documentation comments and moved the slot inside the paragraph element.

[susnux]

/backport to stable7