Offline: fr|databound-select1[appearance ~= search] doesn't work

[ebruchez]

+1 from customer

[ebruchez]

This fails because the submission is synchronous, and we need to make it asynchronous, at least when in the JavaScript environment.

However, the <xf:send> now assume that the actions are sequential. We need instead to react to xforms-submit-done, in the absence of another way of sequencing the submission completion.

[ebruchez]

• consider indication that data is still loading/running in the background

[ebruchez]

Fixing #6216 is needed as we are moving some logic to the component's model.