Automatically focus first interacive element

[nagmat84]

Fixes the regression noticed by @kamil4 on Gitter at Oct 15th 2022 07:17.

The first interactive element was not automatically focused after opening a dialog. There were two independent issues involved:

• Previously we only called select for input elements and text areas which selects all existing text, but does not give focus. We must call focus, too. This regression has been introduced by the change from jQuery in favor of native DOM operations. The old select of jQuery always implies an implicit focus.
• The code was at the wrong position. We can only focus elements after they have become part of the DOM.

[kamil4]

LGTM (tested in Lychee).