Trackpad gesture for F-keys?

For users with the newest Magic Keyboard or other compatible trackpad, it would be nice to be able to use a touch on the trackpad as an extra modifier—for instance, send Escape and F-keys by touching the trackpad while typing ` or 1…0.

No files, tests, or entry points are named. Start by locating the iOS/iPadOS keyboard and trackpad input handling, then determine whether compatible trackpad touches can be exposed as modifiers and define the expected Escape and F-key behavior before implementing and testing it.

Written by the indexing model from the issue text.