Image resizer

[mlewand]

Suggested merge commit message (convention)

Feature: Introduced image widget resizer. Closes ckeditor/ckeditor5#5167.

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Additional information

• Requires Image resizer ckeditor5-widget#94.
• PoC of image resizer.
• Unit tests might fail for the time being as I did not add test coverage yet.

[Mgsy]

Resize doesn't work if there are images in neighbouring table cells.

[Reinmar]

• Tests
  • [ML] Update tests after our recent changes.
  • [ML] Test with responsive images markup.
  • [ML] Verify that srcsetAttributeConverter() doesn't override our width.
• Collaboration examples
  • [PK] Secure resizing for image disappearing during resizing
  • [PK] Use command
  • [PK] Disabling the command should disable the UI
• Misc
  • [ML] Percentage values
  • Fix the table selection handler
  • [PK] Fix the img{width} being float and resizer width being int, which adds this ugly
  • [ML] Make sure building API docs doesn't throw; document the config option and the ImageResize class
  • [PK] Feature guide
  • [KT] Repeate testing
  • [KT] Make sure other browsers are tested
• Followups
  • Handle ESC key ckeditor/ckeditor5-widget#98
  • Split ImageResize to ImageResizeEditing and ImageResizeUI ckeditor/ckeditor5-image#304
  • Improve resize cursor so that it is not overridden during the resize. ckeditor/ckeditor5-widget#100
  • Better detect centered images ckeditor/ckeditor5-widget#102
  • Review other bugs reported by Kacper here.
  • Complete API docs.
  • Rewrite automated tests (100% CC and proper tests for classes). ckeditor/ckeditor5-widget#101

[Reinmar]

Rounding done. It indeed fixed the visual issue.

[Reinmar]

OK, it seems that we've got it. There's a set of followups, but we can merge the functionality which is definitely already functional.