[Bug] Multiple dropzone markers when dragging text and weird selection after mouse release

The title looks weird but I recorded a video https://files.fm/u/u5sqexw48 (their preview is bad, download to watch in good quality)

### The problems

1. When you drag the text, you see multiple dropzones (an arrow with dotted line). I only noticed this in firefox tho.
2. Dropping the text doesn't work, nothing happens. especially if you're dragging a chunk of text to an adjacent area.
3. Weird selections that appears automatically after mouse release or drop. Doesn't go away without another click. This also prevents me from doing another drag&drop action immediately after one whether the previous one is successful or not.
4. Ik this one isn't a bug but one of the most common purpose of dragging text is to place it inside somewhere, not as a block. But the dragging behavior indicates it'll be dropped as a separate block.

### Steps to reproduce
1. Go to editorjs.io
2. Try dragging random texts up and down
3. Drop the text and move your mouse around the editor up/down

_I used the latest firefox (83 and dev) and chrome(87) on ubuntu 20._

I probably noticed part of the problems about an year ago. I wonder if this is already being checked. Thanks