keyboard/altgr: us keyboards converted from X11 symbols

Interesting complete modes found in X11/xkb/symbols/us:
- drix added in xkeyboard-config-2.29~22 (2019-11-14)
- symbolics in xkeyboard-config-2.31~42 (2020-07-27)

Manual helper script mkkeyboard-xkb-symbols to list level 3-4 characters
from source (some cleanup required).