[OptTable] Make explicitly included options override excluded ones

When we have both explicitly included and excluded option sets, we
were excluding anything from the latter set regardless of what was in
the former. This doesn't compose well and led to an overly complicated
design around DXC options where a third flag was introduced to handle
options that overlapped between DXC and CL.

With this change we check the included options before excluding
anything from the exclude list, which allows for options that are in
multiple categories to be handled in a sensible way. This allows us to
remove CLDXCOption but should otherwise be NFC.

Differential Revision: https://reviews.llvm.org/D155729