✨ Setting to change keyboard shortcut to add multiple cursors

### Description

It is now possible to add multiple cursors with ⌃⇧ Click, thanks to STTextView for providing it, which aligns with Xcode. This is what other editors use:

| Editor | Shortcut |
| - | - |
| Xcode | ⌃⇧ Click |
| VS Code | ⌥ Click |
| Atom | ⌘ Click |
| IntelliJ |⌥ ⇧ Click |

Users will probably want a setting to change this shortcut so we should provide a way for them to do this.