Interface Kit: Fix missing Alt key in menu shortcuts

The shortcut detection was working, just not the display of the
modifiers in the menu. I've added back the necessary code to fix
this in BMenuItem.

BWindow does the heavy lifting of preparing the keys and
modifiers. I have changes _FindShortcut() used by BMenuItem to
send the prepared modifiers back to BMenuItem.

Set the parameters raw in the constructor, they will get fixed
up in Install().

I also make sure to use the prepped version of the key and mods
in BWindow::AddShortcut() to remove the old one. This is a minor
update that eliminates an edge failure case of malformed input.

Fixes #19395 a regression from hrev58589.

Change-Id: I4333f89149ff843f92dbffbd53d58ffc2def6760
Reviewed-on: https://review.haiku-os.org/c/haiku/+/8943
Tested-by: Commit checker robot <[email protected]>
Reviewed-by: John Scipione <[email protected]>

headers/os/interface/Window.h

@@ -316,7 +316,7 @@ private:
 			BPoint				AlertPosition(const BRect& frame);
 	virtual BMessage*			ConvertToMessage(void* raw, int32 code);
 
-			void				_AddShortcut(uint32 key, uint32 modifiers,
+			void				_AddShortcut(uint32* _key, uint32* _modifiers,
 									BMenuItem* item);
 			BHandler*			_DetermineTarget(BMessage* message,
 									BHandler* target);