Global settings form for tagging configuration does not work correctly

Problem/Motivation

When using the global configuration form to add settings to individual fields it does not work correctly. The structure of the config entity is different from the one used when setting the configuration individually for each field.

Steps to reproduce

1. Create a new entity with Powertagging field
2. Set the tagging configuration from the field
3. Export configuration
4. Go to the global settings and use the form to override the settings

The structure of the configuration entity is different and not correct:

    concepts_per_extraction:
      slider: '20'
    concepts_threshold:
      slider: '40'
    freeterms_per_extraction:
      slider: '0'
    freeterms_threshold:
      slider: '100'

Instead of correct one:

    concepts_per_extraction: '20'
    concepts_threshold: '40'
    freeterms_per_extraction: '0'
    freeterms_threshold: '100'