Add a config to hide "Enable wireless display" menu

Add config_show_wifi_display_enable_menu to control whether to
display "Enable wireless display" menu at Settings->
Connection preference->Cast.

If persist.debug.wfd.enable is 1, "Enable wireless display" menu will be
shown at Settings->Connection preference->Cast. Add a config to hide the
menu when needed.

setHasOptionsMenu is invoked in onActivityCreated of the parent class of
WifiDisplaySettings. No need to invoke it in onCreate.

Co-authored-by: Jingqiu Zhao <jingqiu.zhao@sony.com>

Test: manual test
Bug: 289532978
Change-Id: I146fb8188e783fed98d9fe56050e384bc4cca052