chore(): improve slate editor

[didd]

Description

• introduce slate editor improvements listed below:
  • if a link is to be inserted in another link then treat it as an ordinary text element
  • if the link to be inserted is at the end of the document then step out of it and insert a space after it
  • step out of a link only if the cursor is at the end of it

Issues that will be closed

Testing

Checklist

• [X] I have read the README document
• [X] I have read the CONTRIBUTING document
• [ ] I have added tests to cover my changes
• [X] All new and existing tests passed
• [X] My commit message follows Conventional Commit Guideline