Grid (Legacy): Fix for RTE drag and drop issue (closes #16591)

[bhcoder]

Fixed #16591

The issue is caused by the upgrade of TinyMCE to v6:

• editors property is deprecated in TinyMCE 4.7 and removed in TinyMCE 6.0 - Use tinymce.get() instead
• registered global editor.settings to reuse the settings once the RTE is reinitialized after drag and drop

[github-actions]

Hi there @bhcoder, thank you for this contribution! 👍

While we wait for one of the Core Collaborators team to have a look at your work, we wanted to let you know about that we have a checklist for some of the things we will consider during review:

• It's clear what problem this is solving, there's a connected issue or a description of what the changes do and how to test them
• The automated tests all pass (see "Checks" tab on this PR)
• The level of security for this contribution is the same or improved
• The level of performance for this contribution is the same or improved
• Avoids creating breaking changes; note that behavioral changes might also be perceived as breaking
• If this is a new feature, Umbraco HQ provided guidance on the implementation beforehand
• 💡 The contribution looks original and the contributor is presumably allowed to share it

Don't worry if you got something wrong. We like to think of a pull request as the start of a conversation, we're happy to provide guidance on improving your contribution.

If you realize that you might want to make some changes then you can do that by adding new commits to the branch you created for this work and pushing new commits. They should then automatically show up as updates to this pull request.

Thanks, from your friendly Umbraco GitHub bot 🤖 🙂

[AndyButland]

Nice, thanks very much for this contribution @bhcoder. I've tested locally and can confirm this resolves the issue that I could replicate before applying this update.