More readable keys in NS menu entries (bug#45502)

More readable keys in NS menu entries (bug#45502)

Each menu entry now has the key binding in a right-aligned column, as
an attempt to improve readability.  Previously the keys were given in
brackets immediately following the menu string.

* src/nsmenu.m ([EmacsMenu parseKeyEquiv:]): Remove.
(skipspc): New helper function.
([EmacsMenu addItemWithWidgetValue:]): Add attributes argument.
Use attributed title string.  Don't special-case Super bindings.
([EmacsMenu fillWithWidgetValue:]): Compute maximum width.  Prepare
attributes for title.