mfenc: Avoid including codecapi.h, fix building in UWP mode with clang

mfenc: Avoid including codecapi.h, fix building in UWP mode with clang

Including codecapi.h and uuids.h in UWP mode doesn't define all defines
properly, ending up with constructs that MSVC silently tolerates, but
that clang errors out on, like this:
    DEFINE_GUIDEX(CODECAPI_AVEncCommonFormatConstraint);

Just avoid including codecapi.h completely and hardcode the last few
enum values we use from there. We already use local versions of most
enums from there, due to older mingw-w64 headers being incomplete.

Signed-off-by: Martin Storsjö <martin@martin.st>