fix(form): support blur for dropdowns

[lubber-de]

Description

non search dropdowns only have a hidden input. Hidden inputs dont support the blur event.
This PR supports that in the way that the change event will also check if it was triggered on a hidden input but on: 'blur' was configured, as the change event will also be applied for hidden inputs

Testcase

https://jsfiddle.net/lubber/tmhrgz41/1/

Closes

#2797

[mvorisek]

The jsfiddle - https://jsfiddle.net/lubber/tmhrgz41/1/ - does not work on my side.

Steps to reproduce:

1. click save
2. errors are set for both fields - expected
3. click input field
4. click somewhere else - error on input field is gone - expected
5. click dropdown field
6. click somewhere else - error on dropdown field is kept - I would expect it gone as well, hence this issue