Tags: Editing a tag on a note creates new unwanted tags sometimes untags note

When editing a tag from the tag bar at the bottom of a note a new tag will be created prematurely before you press any key to finish editing the tag.

Sometimes when changing a tag instead of leaving the tag at the last edit the note will remove that tag

### Expected

When choosing to edit a tag on a note a new tag wouldn't be created until pressing enter, or other key to finish the tag.
That when editing the tag on a note it should keep the final version of the tag name.

### Observed

When you double click a tag at the bottom of a note to edit it, and then rename it to a new tag not yet created, a new tag is created before finishing editing the tag name.

On occasion, once you edit the tag name it removes the tag from the note instead of keeping the last edited tag.

### Reproduced

1. Add a tag to a note.
2. Double click the tag at the bottom of the note screen to edit it.
3. Add characters to the end of the tag name.
4. Notice in the note list on the left that a new note is created before you complete the edit of the tag.
5. Press enter to finish editing the tag.
6. Notice that sometimes the tag is removed instead of keeping the edited tag.


MacOS Catalina
Version 10.15.7
MacBook Pro 16-inch 2019
Simplenote version 2.5

Start by reproducing the tag-bar editing flow described on macOS Catalina with Simplenote 2.5: edit an existing tag, append characters, and press Enter. Trace the tag edit entry point and verify that no new tag appears before editing is finished and that the final tag remains attached to the note.

Written by the indexing model from the issue text.