Sets the character in the alternate title that should be the “keyboard mnemonic.”
An unsigned integer indicating the character in the alternate title that should be marked as the "keyboard mnemonic." If you don’t want the alternate title to have a keyboard mnemonic, specify a location of NSNotFound.
Mnemonics are not supported in macOS.
The setAlternateMnemonicLocation: method doesn’t cause the button cell to be redisplayed.