SCUMM: CGA rendering isn't working correctly across all games

[eriktorbjorn]

This bug report sprang from a failed attempt at adding correct CGA rendering for SCUMM v1 games. See ​https://github.com/eriktorbjorn/scummvm/tree/scumm-v1-dither for details.

Basically, ScummVM doesn't support CGA mode for v1 games at all, i.e. the early Maniac Mansion and Zak McKracken.

But even for games where we support CGA mode, it's not always correct.

For instance, take Maniac Mansion v2. The faces on the character selection screen are supposed to have stripes. But if I fix that, they have stripes in-game as well, which they apparently shouldn't have. I have a feeling it has something to do with actor palettes?

The text color on the character selection screen is incorrect as well. We have some sort of text color translation in place, but perhaps it's for a different game?

And in DOSBox, all games that I've been able to test use a brighter version of the CGA palette. Maybe ScummVM should have an option for that?