Don't try to dispatch alt-something key combos by keycode on macOS

FIX: Make the keymap not dispatch Alt key combos on macOS by key code, because
those are generally used to type special characters.

Closes codemirror/dev#1583

Author: marijnh

src/keymap.ts

@@ -252,6 +252,8 @@ function runHandlers(map: Keymap, event: KeyboardEvent, view: EditorView, scope:
     } else if (isChar && (event.altKey || event.metaKey || event.ctrlKey) &&
                // Ctrl-Alt may be used for AltGr on Windows
                !(browser.windows && event.ctrlKey && event.altKey) &&
+               // Alt-combinations on macOS tend to be typed characters
+               !(browser.mac && event.altKey && !event.ctrlKey) &&
                (baseName = base[event.keyCode]) && baseName != name) {
       if (runFor(scopeObj[prefix + modifiers(baseName, event, true)])) {
         handled = true