buttons field formatter doesn't show the current state

I have created an MR against the latest development versions with the following improvements compared to the latest patch.

• Removed redundant code for getting the state label, provided by the field type plugin.
• Set default value to FALSE because that is the current behavior. It would be an unexpected change for applications updating the module that may even go unnoticed, so I think developers should intentionally enable this. If decided otherwise, this should be pointed out in the release notes.
• Small improvement in the settings form element description.
• Removed the "Current state:" prefix when rendering the state. Using the field label is clear and consistent in styling; the label is clear that this is the state and it is clear that the buttons represent the available transitions thus I see no ambiguity. I have tested with either the "inline" and "above" label display and it works fine with standard admin themes such as Claro.

Uploaded a screenshot of how it looks like with commerce_license.