KeyboardEvent key values in keyboard_maps.dart have mappings for 'Escape' but not for the older 'Esc' key values.

These values were used by older IE and Firefox browsers, and are still being generated by the Cobalt browser.

(Specifically, this is causing problems when running a Flutter-Web app on Cobalt and using the back button on the TV remote. The KeyboardEvent generated by Cobalt has an 'Esc' key value, which then does not get interpreted by Flutter as an LocalKeyboardKey.escape event.)

See the note on the 'Escape' value here:
https://developer.mozilla.org/en-US/docs/Web/API/UI_Events/Keyboard_event_key_values#ui_keys