[input-tel-dropdown] correctly compute dirty state

[tlouisse]

Expected behavior

will not become dirty bc/o model-value-changed event of child FormControl (SelectRich)..

Solution

Needs to be fixed in FormControlMixin for all FormControls that are "endpoints" (cq. repropagationRole is 'child'). Fix in the making here, needs to have all tests green again: https://github.com/ing-bank/lion/pull/1719