[Clang][Docs] Consolidate option hiding in ClangOptionDocEmitter

Update the `hasFlag` check to account for an Option's groups to better
match how the option parsing logic works, and instead of checking if a
group has include/exclude flags just check if there are any visible
options in it.

This cleans up some the empty sections that are currently emitted in
clang's option docs.

Differential Revision: https://reviews.llvm.org/D157146