Feature request: Drag-and-drop text in editor

Requested in 2911722-zen. User says this is a system thing in OSX and they were surprised it's not supported in Simplenote. I only tested in the Notes app, which does indeed allow you to select a block of text and drag it to move.

The issue names no files, tests, or editor entry points. Start by locating the macOS editor implementation and examining how text selection and movement are currently handled, then compare the expected behavior with the Notes app. Done means selected text can be dragged to a new position in the editor without breaking existing editing behavior.

Written by the indexing model from the issue text.