Fix: edit with multiple editors ck5

[carla-at-wiris]

Description

When multiple CKEditor instances are rendered within a single CKEditor context, opening the MathType popup from any editor and then clicking Cancel does not restore focus to the editor that opened the dialog.

Instead, focus is transferred to a different editor, typically the one from which MathType was previously opened.

This PR fixes the issue by recalculating the current instance when opening an existing formula.

• Related Kanbanize Card: Link to KB-62608

Type of Change

• Bug fix (non-breaking change which fixes an issue)

Checklist

• My code follows the style guidelines of this project ( Run yarn lint to check)
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (if applicable)
• My changes generate no new warnings or errors
• I have added tests that prove my fix is effective or that my feature works (if applicable)
• New and existing unit tests pass locally with my changes

How should be tested? (Manual or Automated Tests)

• Modify the CKEditor5 demo to add multiple instances
  • Copy the code from line 30 to line 68 on the file demos/html/ckeditor5/src/app.js.
  • Paste it after line 68. Paste as many as editors you want.
  • Change the ID on the first line to uniquely identify the editor.
• Modify the HTML code to include the new editors
  • Copy the code from line 12 to line 14 on the file packages/res/demos/index.html.
  • Paste it after line 14. As many as editors you want
  • Change the div ID to match the ID's you created for the CKEditor's before
• Now that the demo is ready, le'ts build and start it:
  • Clean all dependencies with git clean -dfx
  • Install the dependencies with yarn
  • Build the CKEditor package with nx build ckeditor5
  • Start the ckeditor demo with nx start html-ckeditor5

[ncornaglia-at-wiris]

Pues doy el aprobado y rezo que nose rompa nada extra