Make base64 encoded images collapsible

[tbsbdr]

embedding images via base64 is generally awesome ❤️ thanks for your great work!

Would you approve a pullrequest that would do the following?

Current Behavior

• paste an image
• base64 code makes me scroll a lot to get before/after the image in the text

Expected Behavior

• paste an image

• base64 code is collapsed by default

• easily get before / after the base64 encoded image

Visual

https://github.com/nhn/tui.editor/assets/26610733/eef6961f-0809-4861-82f6-25b6b965801e

partly relates to https://github.com/nhn/tui.editor/issues/2860