Rename MCFiltersEvalUniEncode and MCFiltersEvalUniDecode

The overloads of this function have been re-named to better reflect their operation {To,From}{Native,Encoding}
[[ Bug 10932 ]] Added override to MCField::settextatts to allow preventing relayout.
[[ Bug 10932 ]] Added handling for P_UNDEFINED to MCField::settextatts to just force a relayout in the same way as if a prop was set.
[[ Bug 10932 ]] Used new settextatts() semantics to speed up setting P_FLAGGED_RANGES.

Conflicts:
	engine/src/fields.cpp