Fix horizontal scroll direction for macOS (#9022)

macOS uses negative values to represent scrolls to the right, while
Flutter expects the opposite, so flip X deltas.
https://dart.googlesource.com/external/github.com/flutter/engine/+/e1599ccd3f89943a11c89ac8a31cc7d3edd72073
1 file changed
tree: 4969c58768952cae47a59119fd0f119a8db4b0f0
  1. commits.json