For required tags, allow child tags to satisfy the requirement

[cellio]

meta:289410

A category can specify a set of required tags, such that a top-level post must use at least one tag from the set. Meta does this for discussion/feature-request/support/bug. Some communities would like to use required tags to require some child tag -- for example, a programming-language tag on Software Dev that can be satisfied with C++ or Python, or a locale tag on a hypothetical law or workplace community that's satisfied with Canada or EU or New York.

When checking a post for required tags, can we check not only the exact tags but their parents up the chain?

I'm setting the priority low for now because we don't have an active request from a community that I know of, but it's something that could be used if we had it so it's worth considering.