Allow customizing prefix and suffix widgets for the searchbox using builder functions

[jagged3dge]

Is your feature request related to a problem? Please describe.
There could be situations when the app designers want different look for the default search bar that appears on the map.
For example, this could be a client-approved mockup from the designers:

From the code I can see that the search box is hardcoded to have an IconButton as the prefix and a simple SizedBox as the suffix.

Describe the solution you'd like
It'd be really great to have this flexible enough to allow for custom widgets to be displayed before and after the autocomplete field.

Describe alternatives you've considered
The current alternative is to fork the repo and create these myself.

[martin-braun]

We need an autoCompleteSearchBuilder (and perhaps an autoCompleteSearchPredicionOverlayBuilder) that allows to build an own search bar (and prediction overlay) with the most customization potential.

If this was provided, one could simply build own components for the UI, while the logic is still contained in the AutoCompleteSearch component.

[artkinx]

We need an autoCompleteSearchBuilder (and perhaps an autoCompleteSearchPredicionOverlayBuilder) that allows to build an own search bar (and prediction overlay) with the most customization potential.

If this was provided, one could simply build own components for the UI, while the logic is still contained in the AutoCompleteSearch component.

@martin-braun Can I look into this?

[martin-braun]

@artkinx I'm currently trying to keep this in maintain mode only, as I am too busy to further develop this widget. A PR would be much appreciated.