Allow fallback for unsupported browsers

Problem/Motivation

Firefobx mobile & edge mobile don't work / support datalist.
Provide a fallback method

Proposed resolution

use autocomplete in these cases.

Remaining tasks

Implement it

User interface changes

'#autocomplete_route_name' => ''
'#autocomplete_route_parameters' => [

provide these settings to the element.

Optional "allow_fallback" can be used to override in case of ... emergency?