Separate configuration of CE field formatters and display components

Core field formatters store into entity-display component something like

component-of-field:
   type: <formatter-id>
   settings: <array-of-formatter-settings>

But core field formatters, they auto-generate some plugin configuration which looks the same. So their plugin configuration is something like:

configuration:
   type: <formatter-id>
   settings: <array-of-formatter-settings>

But in current 3.x branch our ce-field-formatters are having settings and configurations as same thing:

component-of-ce-field-formatter:
   formatter: <formatter-id>
   settings: <array-of-formatter-settings>

configuration:
   formatter: <formatter-id>
   settings: <array-of-formatter-settings>
   custom-config: <value>

What is very similar. but our plugins can change configuration, not only settings.
Maybe we need to move it to clear separation:

component-of-a-formatter:
   formatter: <formatter-id>
   configuration: 
     settings: <array-of-formatter-settings>
     custom-config: <value>

quick draft

added some test-coverage to make sure config is passed through to the formatter correctly also. works now, MR is ready

Merged!

Automatically closed - issue fixed for 2 weeks with no activity.