Pasting additional text into tag editor results in two tags creation

The reason for the issue lies in the fact that the tag pasted from the clipboard submits the tag.

For the record, pasting text into tags editor in Electron does not submit a tag.

### Expected
If there's an existing text in the tag editor, and the user pastes additional text into the tag, the pasted text should be appended to the existing one.

### Observed
Instead of being appended, two tags are submitted: with the previously existing text, and with the pasted text:

https://user-images.githubusercontent.com/73365754/128510073-96ebd0d8-27a4-4127-971c-a46b2b28de9f.mov

### Reproduced
1. Create a new note
2. Place `text1` into the clipboard (just a single word for simplicity)
3. Start entering `text2` in tag editor, and then paste `text1` ~> this action will create `text2` and `text1` tags

Make|Model|macOS Version|App Version
-|-|-|-
Apple|MBP 16"|11.3.2|2.14 (11239)

Reproduce the issue in the macOS tag editor using the listed text1/text2 steps, then trace the editor's paste handling to see why pasted text submits the existing tag. Done means pasting additional text appends it to the current tag and creates only one tag, matching the expected behavior.

Written by the indexing model from the issue text.