EditableInput: Increment on Drag

The text input fields could be draggable, as with applications like After Effects.
- On :hover, a east-west cursor is shown (north-south if more appropriate for the given layout).
- On drag originating from the field, the value is modified by +/-1 at an interval that scales with the vector's magnitude. On account of typical input precision, the rate should be slow (1 per 500ms?) for a generous margin near the field (estimated: first 8-10px).
- On mouseup, the timeout is cancelled so as to not increment after gesture ends.
- It may be necessary to lock out text-selection until mouseup (or focus) inside the field. Many apps that support this have an edit state to resolve these conflicting interactions.