3c93ad4c5 [web] Resolve OS as iOs for iDevice Safari requesting desktop version of app. (flutter/engine#25957) (#82300)

Re-land:  Allow users to pass in Xcode build settings as env variables to flutter build macos FLUTTER_XCODE_  (#82298)

I noticed that tab traversal stopped working on iOS when #73440 was landed.

It seems to be that the control characters were excluded from the list of logical keys, and so they ended up being generated values.

This PR just adds "Enter" and "Tab" to the list for both macOS and iOS.

This reverts commit d28737ee.