Issue #3618463: Allow null map provider on GeolocationMapFormatterBase

Luisrequested to merge
issue/geolocation-3618463:3618463-typeerror-cannot-assign into 4.x

Fixes TypeError in GeolocationMapFormatterBase::__construct() when map_provider_id is set but the plugin is missing. Property matches the widget: ?MapProviderInterface $mapProvider = NULL.

Closes #3618463

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