SCUMM: Improve non-Towns CJK text rendering

These commits fix various v7/v8 CJK related problems:
- Completely broken Korean text rendering in The DIG. (Taiwanese or Chinese seems to be broken as well)
- v7+ CJK games have incorrect line break, leading to incorrect positioning and text disappearing.
- Korean The DIG renders text shadow different than the original version.
- Korean COMI doesn't have any text shadow as opposed of the original.

This introduces new base class CharsetRendererPC for CharsetRendererClassic and CharsetRendererV3 to share text rendering code.

Note regarding hackish NutRenderer/SmushFont fix:
It seems the original interpreter does the similar thing, but it looks hacky. :P
Maybe we could extend (and rename) current FontSJIS class which has the ability to draw text with shadow, to support Korean or Chinese and use it eventually.

Tested with:
- The DIG (English / Korean)
- COMI (English / Korean)
- Monkey Island 2 (TOWNS Japanese / English)
- LOOM (English Floppy / TOWNS Japanese)