[chore]: Update STTextView to `0.5.3`

[thecoolwinter]

Description

Updates STTextView to 0.5.3, accounting for a couple API changes & depreciations.

Known issues:

• Editing with multiple cursors loses focus of all but the top-left cursor after applying the edit.

Also includes a tiny fix for a runtime error when publishing cursor position, and a fix for a rare crash to do with string indexes. (STTextViewController+Cursor.swift).

Related Issues

N/A

Checklist

• [x] I read and understood the contributing guide as well as the code of conduct
• [x] The issues this PR addresses are related to each other
• [x] My changes generate no new warnings
• [x] My code builds and runs on my machine
• [x] My changes are all related to the related issue above
• [x] I documented my code

Screenshots

Copy-paste attributed text

https://user-images.githubusercontent.com/35942988/234060270-82170964-c1b1-4dbf-bea2-3d6108857b3f.mov

Multiple cursors (control-shift click)

https://user-images.githubusercontent.com/35942988/234060289-f564f8be-ae57-482d-9037-9fd144591a1c.mov