Fix/aut 3961/taofurigana ruby rt not focused

[olga-kulish]

Related to https://oat-sa.atlassian.net/browse/AUT-3961

Use with:

• Fix/aut 3961/taofurigana ruby rt not focused tao-core-shared-libs-fe#42
• Fix/aut 3961/taofurigana ruby rt not focused tao-core#4160

Deployed on:

Issue

In Chrome, in Authoring add a ruby tag --> <rt> is not focused automatically, so author can't type his furigana. If you press "arrow-right" to move cursor, then it's focused.
Fine in Firefox.

Probably, the cause of the issue is not a change in our code, but a change of native browser behavior for contenteditable in newer versions.

Fixed by moving cursor position one symbol after: ckeditor docs.

TODO:

• test on Safari

Other issues:

I'm pretty sure these issues existed before too (= always). Still, let's at least take a look.

• Placeholder   (<rt>&nbsp;</rt>) is never removed, even after user enters his furigana, it stays in itemData
  • tried to use CKEDITOR.dom.selection.FILLING_CHAR_SEQUENCE instead, <rt> is fine then, but this sequence is sometimes appended after ruby?
  • should we use \200B (zero-width-space) instead, or even trim it in item-runner?
  • can we somehow modify DOM and remove it on blur for example? If taofurigana was an inline widget with downcast/upcast converters, it would have been possible. But it's a native html tag, so not sure.
• If you remove this   placeholder by pressing Del/Backspace, and don't enter any other text, you can no longer return and edit your ruby, even though it stays in the markup and itemData.
• Strange cursor position when typing (at the end of <rb>, away from where the actual typing inside <rt> happens): browser contentediatble issue, try in playground: https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/contenteditable : <div contenteditable="true"><p><ruby><rb>とても長い言葉</rb><rt>&nbsp;</rt></ruby>で話す<ruby><rb>のわ楽しい</rb><rt>たのしい</rt></ruby>かもしれない</p></div>. Check ruby-align.