CodeMirror defers Enter on iOS (and Chrome Android): the real keydown is
captured without running the keymaps and the keymaps then run against a
synthetic keydown that dispatchKey builds from the key name alone, with
no modifier keys. The composer's Shift+Enter thus arrived as a plain
Enter, and on devices where Enter sends (iPad Safari/PWA, where the
desktop layout applies) it submitted the message instead of inserting a
newline.
Record the real Enter keydown's shift state on the view's contentDOM and
restore it onto the deferred synthetic event before the caller's
onKeyDown policy runs, so Shift+Enter means newline again on every
runtime. Plain Enter behavior is untouched: on iOS it still follows the
same deferred path it used before this change.
Fixes#2558
Serhii Dziupin
7ff86a3bc7