Add cbuild subcommand to get template dependencies

[triallax]

sometimes i want to do some work on a package outside of cbuild, in which case i'd like to install the package dependencies (all of *depends basically) in my host system, which can be annoying because of the extra double quotes and commas and stuff, particularly for stuff with many deps like gk4

so it would be nice if cbuild had a subcommand e.g. print-deps which would print a space/newline-separated list of dependencies; then for my particular use case i can use doas apk add -- $(./cbuild main/gtk4 print-deps) to install gtk4's dependencies in my host system

maybe this could be generalised as well to e.g. configure args, but i don't have anything concrete in mind for that

[triallax]

hm actually, virtual packages would introduce a slight complication here because they can't be passed to apk as-is

for these we can maybe use the package after the ! or something, idk