"boot verbose", "single user mode", "ACPI" and more are now stateful boolean
menuitems rather than direct action-items.
A short-coming in this new menu system is that when a user sets a non-default
value in loader.conf(5), this non-default state is not reflected in the menu
-- leading to confusion as to whether the option was taking effect or not.
This patch adds dynamic menuitem constructors _and_ the necessary Forth
callbacks to initialize these stateful menuitems -- causing the aforementioned
menuitems to adhere to loader.conf(5) settings.
PR: bin/172529
Approved by: adrian (co-mentor)
MFC after: 21 days
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