bsdinstall: Use package sets for pkgbase install

Update the pkgbase component selection dialogue to take the components
list from the meta-package sets available on the install media, except
for "kernel" which is still handled magically.

Always install "minimal", and by default select "base", "kernel-dbg"
and any libcompat sets (e.g., lib32) if they're available.

Replace the various "dbg" options with a single "debug" component that
installs the debug symbols for all the components the user selected,
except for kernel since we handle that separately and it's common to
want kernel debugs symbols without userland debug symbols.

MFC after: 3 seconds
Reviewed by: emaste
Differential Revision: https://reviews.freebsd.org/D52558

(cherry picked from commit 55ba5550d25d58144007ae02b07450ec8cda7ee5)