t/ckeditor5/1457: Implemented Font Color and Font Background Color features

[msamsel]

Suggested merge commit message (convention)

Feature: Implemented Font Color and Font Background Color features. Closes ckeditor/ckeditor5#1457.

---

Additional information

• CI: https://github.com/ckeditor/ckeditor5/compare/t/1457?expand=1

PRs:

• t/ckeditor5/1457: Moved the eraser icon from ckeditor5-highlight. ckeditor5-core#169
• t/ckeditor5/1457: Moved the eraser icon to ckeditor5-core ckeditor5-highlight#38
• t/ckeditor5/1457: Added styles for color features in ckeditor5-font and ckeditor5-ui ckeditor5-theme-lark#222
• t/ckeditor5/1457: Implemented ColorGridView and ColorTileView components ckeditor5-ui#474

[jodator]

My 2 cents:

• consider different keyboard navigation #26

• white color has no focus outline on keyboard navigation:

  
  (the colors on buttons were only for testing purposes)

• currently selected color has no focus outline on keyboard navigation:

  

• I don't like FontBackgroundColor* name. For me FontBackground* would be enough :) But it's rather meh..

[jodator]

OK. I think I'm done with reading all that :D

[mlewand]

Corrections

The default value registers 15 colors:

changed to:

The default value registers following colors:

It's better not to mention too much details of value that is right below, that way we reduce thw chance that someone edits the listing alone (adds/removes some colors) without updating this particular line.

I have simplified manual test description (it was basically duplicating the editable contnet).

Issues

• The "recent/document" colors feature to pick up pasted/preloaded colors is missing, but this should not be blocking this PR extracted to #28.
• hasBorder property won't work properly, as here the assumption is that the skin will be bright (as it's applied to bright colors). It won't work without reconfiguration with dark themes.

minor:

• There's no string value example in FontBackgroundColorConfig.colors (and respective font color struct).
• FontBackgroundColorConfig and FontColorConfig implement identical interface and both have the same default values. It would improve DRY factor to have a common interface for both features. I see that now the listings differ in both, but having common interface should simply mention both configuration names.

Above things will be extracted to a separate issues not to block this PR.

[mlewand]

Ok all the things extracted, PR is ready to land on master branch. I'll merge it in few mins.