Translate synthetic physical-key events with characters(byApplyingModifiers:).
This preserves current-layout and Command-table behavior while avoiding a
duplicate direct UCKeyTranslate implementation in Swift.
Text Input Sources APIs are not thread-safe, but shortcut translation could
be called outside a declared main-actor context.
Mark keyboard layout and shortcut conversion as main-actor isolated, update
their tests, and dispatch key-sequence UI notifications to the main queue
before translating their shortcuts.
Translate printable physical keybindings through the current macOS
keyboard layout before assigning menu key equivalents. Previously these
bindings could not be represented because SwiftUI shortcuts are
character-based, so actions such as super+backquote had no native menu
shortcut.
Keep native keycodes as dispatch identity so translated display characters
do not change physical semantics or precedence over Unicode bindings.
Refresh shortcuts when the input source changes, and prevent AppKit from
transforming equivalents that are already localized.
Fixes#4539
AquaSKK is a Japanese IME (Input Method Editor) for macOS. It uses
keyboard inputs to switch between input modes. I don't know any other
IMEs that do this, but it's possible that there are others. Prior to
this change, the keyboard inputs to switch between input modes were
being sent to the terminal, resulting in erroneous characters being
written.
This change adds a check during keyDown events to see if the input
source changed _during the event_. If it did, we assume an IME captured
it and we don't pass the event to the terminal.
This makes AquaSKK functional in Ghostty.
