Provide migration path for colorbutton configuration

I have prepared a PR with the following changes
- FontSizeAndFamily plugin update for "colorbutton" migration
- updating FontBackgroundColor and FontColor plugins so that default colors are used when empty settings (behavior from "colorbutton")

Here is the patch with these changes

Hi. I tried the upgrade from CkEditor4 to CkEdtior 5, with colorbutton and preconfigured colors.
The site is running Drupal 10.2.1. During the upgrade from CkEditor4 to CkEditor 5 using ckeditor_font:2.0.x-dev with the 3306246-4.patch.

However I get an error and the upgrade fails with message:
"

Error message
Oops, something went wrong. Check your browser's developer console for more details.

"

In the logs i find the following error:
AssertionError: assert(count($cke5_plugin_settings) === 1) in assert() (line 484 of /var/www/html/web/core/modules/ckeditor5/src/SmartDefaultSettings.php).

Adding some debug before the assertion test before line 484 in web/core/modules/ckeditor5/src/SmartDefaultSettings.php, gives me:

$cke4_plugin_id="colorbutton"
and

$cke5_plugin_settings=Array
(
    [ckeditor_font_font_color] => Array
        (
            [font_colors] => #474994
#E7B059
#E8BBBA
#A0CCCB
#ff0000
        )

    [ckeditor_font_font_background_color] => Array
        (
            [font_backgroundcolors] => #474994
#E7B059
#E8BBBA
#A0CCCB
#ff0000
        )

)