Fix: reset search filter input after adding selected entity data

[xetra11]

In order to get access to the search field element I needed to invoke a weak pointer to workspace. However I don't feel that's the intended way to have access to another element inside an element action callback.
@BrentFarris
Maybe you can direct me to a kaiju conventional way?

entitySearchFilter, ok := dui.workspace.Value().Doc.GetElementById("entitySearchFilter")
if ok {
entitySearchFilter.UI.ToInput().SetText("")
}

[BrentFarris]

In order to get access to the search field element I needed to invoke a weak pointer to workspace. However I don't feel that's the intended way to have access to another element inside an element action callback.

The current flow, at the moment, for these UI elements is to store a reference to that UI element in the setup function. Then you'll just have it as a member of the object and won't need to pull it from the DOM.

This adds another member, but that's fine since there is only ever 1 of this particular struct created.