keyboard/altgr: expected greek alphabet transliteration

keyboard/altgr: expected greek alphabet transliteration

Hardcode a mostly phonetic glyph map, overriding default letter names
so eg theta Θ matches Q not H (recognising spacecadet instead of eurkey).

Fixes spacecadet where everything is at expected keys except for ϑ and ς,
and eurkey allowing υ/φ/χ but not θ.