fix(#1545): Split Editor Causes Hang

[thecoolwinter]

Description

Fixes a bug where opening the same file in a split editor would cause an infinite hang. The hang was caused by both editors in the split sharing a single published cursorPositions variable. When one editor was unfocused, it would try to set that variable to be empty, but it was immediately updated by the newly focused editor to contain a new cursor position. This led to an infinite loop of both editors attempting to update the shared variable.

To fix, I've added the notion of an 'instance' of an editor. There's now three levels of abstraction for a single editor:

• CEWorkspaceFile: Basically a pointer to a file, does not read contents.
• CodeFileDocument: For reading / writing a file, contains the contents of the file.
• EditorInstance: Manages a single visual instance of an editor, including published cursor positions or other injected objects.
  The editor manager now manages editor instances instead of files.

I'd have liked to have #1564 merged before this one, but there are other problems with the CI making it take longer than expected, so this can be merged before that.

Related Issues

• closes 🐞 Opening file in split editor causes infinite hang #1545

Checklist

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

Screenshots

N/A

[0xWDG]

LGTM

[austincondiff]

Great work! Love the new EditorInstance class!